CSA accuses me of fraud despite their mistake

My ex ran off with another woman when my daughter was 6. This was a bolt from the blue and he left us without any money. He had a capital sum so I was advised by a solicitor to take him to court for a lump sum. He kept delaying proceedings and by the time it got to court the money (proceeds from our business sale) had disappeared. So I was advised to apply to the CSA. For years I got nothing at all, although he was a self-employed film director/script writer and was travelling the world and having expensive holidays with yet another woman. The CSA admitted to me that they knew he was lying about his income, but could not do anything as he was self-employed.

After many years the CSA finally caught up with him and agreed he could pay a laughable £5.20 a week, by this time my daughter was 12. He paid the CSA (in cash) weekly. When my daughter was 19 the CSA said he had to carry on paying at the same rate until the 6 years arrears had been paid. This he has done (still in cash) on a weekly basis.

Last year I was informed he was terminally ill and the CSA said that when he died any unpaid arrears would come out of his estate to me.

This week the CSA phoned me and told me that I had committed fraud by not telling them my daughter had had her 19th birthday. I told them that they had arranged the payment of arrears and they denied this. I was then told that the full amount of debt to me had been paid off by January of this year and that I would have to pay back all money paid since then. I was furious to say the least that I should be accused of fraud.

Yesterday I got a demand for £1307 for all payments since her 19th birthday (i.e. 5 years @ £5.20 per week).

Firstly if the payments were not arrears, why would he have paid them? He knows how old she is. Secondly why, when I have had many discussions about his payments of the arrears since she was 19 have they accused me of dishonesty and fraud?

I am on a basic state pension and no way can I afford to pay this money back. My ex is still alive despite being terminally ill and they have now sent him a cheque for £1307, which, I am sure he is delighted to have. All the arrears received from him have been spent on our child. She is a single parent of a disabled 5 year old born the week she was 19 and I have bought them food, clothes and a car so she could take a degree and do her teacher’s training. She stopped being a full time student on 30 June this year.

The CSA tell me that my ex has claimed that I have deceived them as to my child’s age, but they have her date of birth and they claimed they never looked at it during any of our phone calls!

They have upset me so much. I am so worried. I have been getting chest pains since their call and letter and keep crying. I have to go through their appeals procedure now and have no faith in that. I have never committed any fraud and took all payments in good faith. How can the CSA twist things around like this?