They've just f*cked mine up too -just spent 30mins on the phone trying to get someone to tell me why (and failed)... Not to the extent as detailed here but we have only just finished paying back (by accepting reduced payments) the £8k they overpaid us 5 years ago . That was back in teh days when I just let things like this ride. Not this time mate. Off to start another thread about it as I have abit of a different question.
I think you may only have 30 days from the date of the last letter to appeal though. Ring them and tell them you want to dispute it.
Agree with other posters though - have just got this off the hmrc website wrt my own problem:
Q. Do I have to pay a fine/penalty/interest?
A. You must tell us about any changes to your work, childcare or household as quickly as possible. If you don?t tell us, you may receive more money than you are entitled to and you might have to pay back the money as well as a £300 penalty.
These changes include:
You and your partner stop living together as a couple and you had been receiving joint tax credits
You start living with a partner as a couple and either or both of you had been receiving tax credits separately
You stop paying for childcare for at least 4 weeks in a row
Your weekly costs for using childcare reduce by £10 a week or more for at least 4 weeks in a row
There is a change in your working hours
The number of children for whom you can claim family support changes.
Q. If I have been paid too much tax credit, how much money am I expected to pay back?
A. If you told us about any changes to your work, childcare or household as quickly as possible and we did not do anything to change your tax credits, so you have received too much tax credit, we will not expect you to pay back the extra money you have received. However, if you do not tell us about a change within the given time, we will expect you to pay back the tax credit overpaid.
Q. If I have been paid too much tax credit how will it be collected from me?
A. Normally if we find out about the overpayment in the same year we will try to get the amount overpaid back by reducing your tax credits award for the rest of the year. If this is not enough, we could adjust the next year's award. If there was no further entitlement to tax credits we could adjust your PAYE code or look at other normal ways.