I moved into my apartment as a single occupier in 2005. Since then Thames Water has charged me about £980 a year. It only became apparent that this is massive overcharging after the residents in my block began swapping notes recently.

I now realise that I should have been paying £165 a year on the single-occupier rate. The £980 is a fixed charge, based on the rateable value of the property (set in 1973) and not on the amount of water I use. Thames Water says that this value was frozen in 1990.

I cannot have a water meter fitted because the building is not suitable. Thames Water cannot guarantee that the new charge will be backdated to my last bill in April. I estimate that I have overpaid by about £3,260.

Kate Upton, London

What your letter highlights is that many of us do not have a clue how much water bills should cost, nor how to bring them down.

This suggests that the water industry has failed to educate customers. You were paying six times your new annual charge — not a small discrepancy. It is astonishing that no one at Thames Water told you that £980 a year is steep for anyone (the average is £300), nor advised you of ways to bring it down.

The “rateable value” system of assessing water usage is horribly inaccurate. Being on a meter makes sense, unless you have more people in the house than bedrooms, in which case it may work out more expensive. Thames Water says that it has been telling customers this “for years”. It clearly hasn’t been shouting loud enough.

Troubleshooter managed to persuade it to backdate your new charge to April. Ofwat, the regulator, says that water companies are unlikely to backdate farther than the previous bill. This would not be fair, it says, because they do not ask customers who have underpaid for years to pay back the money they owe. This is a bit of a non sequitur, given that ultimately it is the water company’s fault.

However, there is a very strong case for backdating bills in cases such as yours, where you knew that you could not have a water meter fitted because of the building, and thus might not have thought it worth mentioning. Thames Water should have told you that an alternative to a meter is an “assessed household charge” (worked out according to the number of bedrooms) way before it also introduced the single-occupier tariff (which should have been introduced a long time ago).

The lack of an attempt to communicate these things to you and others is a gross oversight not only on the part of Thames Water, but also Ofwat. It says that guidance has been in place since 1999 for water companies to provide details of the options with bills. Ofwat also monitors the companies to make sure that they do this. This effort is too little and a few thousand pounds too late for many households.

My daughter is trying to obtain a mortgage with Abbey. She has an approval, but Abbey checked her credit record with Experian, the credit reference agency, and found an unpaid Abbey credit card debt. Abbey checked the file on May 10, but the debt was cleared on May 11. Abbey will not give the mortgage until the “unpaid debt” is removed by Experian, but said that there was an IT systems issue between the two.

The solution seems simple, as the mortgage and credit card are both with Abbey. My daughter is about to lose her property purchase.

Chris Winter, by e-mail

Experian’s credit files are updated once a month. If there is a change, it is up to the lender to call the agency. If the customer calls Experian, it can then query the claim with the lender.

Troubleshooter has no idea what Abbey was talking about when it cited IT system breakdowns. It sounds like one of those standard “don’t blame me, blame the computer” excuses.

Your daughter’s credit file has now been updated by Experian and Abbey has offered you £200 as a gesture of goodwill.

Weeks ago I received a parking fine demand from Leeds City Council (LCC). I have never been to Leeds and at the time the ticket was issued I was 280 miles away in Worthing. My car was parked in a pay-and-display space while I had dinner and went to the theatre.

Although the registration number that LCC quoted was correct, the vehicle colour was stated as blue, but my car is green. I sent evidence that I was not in Leeds and that my car is a different colour, but LCC says that I could have “resprayed the car”. It also says that me being in Worthing is irrelevant as somebody could have “borrowed the car” and driven the 560-mile round trip while I was at the theatre.

LCC is now demanding that I send my tax disc number to prove it is different to that recorded by the parking enforcement officer.

Karen A.Dunn, Worthing

A fraudster has used your registration number on a car that is not yours, probably to disguise a stolen vehicle. This is an increasing problem in the recession, but one that city councils are ignoring. Send the tax disc number and then contact the police. And remember in future that the parking adjudicator is easier to deal with than local councils.

To tell us your problems, visit timesonline.co.uk/troubleshooter or write to Troubleshooter, Times Money, Times House, 1 Pennington Street, London E98 1TB. Owing to the high volume of correspondence, Troubleshooter cannot guarantee individual replies.

Readers to the rescue

My grandmother left her jewellery, most of which was costume, to me and my siblings. One of the necklaces I chose, I discovered later, is made of real diamonds and worth a lot of money. Should I tell my brother and sister? When we divided my grandmother’s possessions it caused a lot of heartache and arguments.

Michelle Wilson

I think you should tell them. Most secrets come out in the end and I would rather share a surprise windfall than lose the friendship and respect of my family. If your grandmother wanted you to share her possessions, then the whole family should benefit.

Olivia Mitchell

It was your good fortune in choosing it, just as your siblings chose the items that they wanted. I believe that once something is given and accepted as a gift, which this was, the future care and value of it belongs to the recipient.

Ms Brennan

£25 voucher winner

You already feel a little awkward about your lucky choice of granny’s jewellery. I’m a very old granny (89) and my advice is to tell your siblings. They will be amazed, delighted and, who knows, they might also have discovered treasures. What a party you will have.

P. Ruddy

If you plan to sell the necklace, keep 50 per cent yourself and split the rest with your siblings. Send them a cheque in the post with an explanatory letter. They are likely to be so grateful with the thought and cheque that they would be unlikely to query the sale amount. If they do, simply state that it was their fair share of the proceeds.

Toby Wilbraham

What do you think your grandmother would have wanted you to do? I would come clean. Perhaps you could have the diamonds taken out of the item and made into individual items for you all. You will still have the sentiment but also a unique piece of jewellery to remember your grandmother by.

Alison Gorrie

Can you help?

E-mail troubleshooter@thetimes.co.uk with your answer to the following problem for the chance to win a £25 John Lewis gift voucher.

My partner and I were invited to spend a week with another couple, who have been close friends of ours for some time, in their holiday home in Spain. We were delighted to accept and had a wonderful time. But on our return home we received an e-mail listing money we owed them: half the cost of gas, electricity and the cleaner, plus money towards car hire (they drove us to the supermarket and beach during our stay).

While we were in Spain we split the cost of food and drink, and took them out for a nice meal on our final night to say thank you. We paid up for fear of appearing rude, but now feel slightly aggrieved. Should we say something?

Jason Gallagher

On the bright side

Alison Everness, of Dorking, Surrey, writes: “I ordered money for my holiday to South Africa from Barclays on a Sunday and was told that I could collect it at 3pm on Wednesday and did not need to pre-order traveller’s cheques. I arrived at my branch only to be told there was no cash or traveller’s cheques available.

“In a panic I visited a small post office branch where I was offered currency and traveller’s cheques on the spot. I can’t vouch for the competitiveness of its rates, but the service makes the Post Office my first choice for foreign currency.”