Advise needed

I have been divorced from my ex for 17 years, we have 4 children. I have received a bill from the CMS for over £10,000 (this is now being taken from my earnings on a monthly basis) which according to them is debt from the CSA from 2012. I did receive this in 2012 and I questioned the validity then, and still do. I paid my ex directly and have receipts and bank statements to verify this but the CMS state that this is debt from the CSA and cannot be incorrect. I have a letter from my ex's solicitor asking me to pay my ex directly into her bank account from 2009 and I paid the CSA directly from 2010. Also I had two of my four children living with me for most of this period, but I never made any claim as I took fatherhood seriously

My question is, from a legal stand point, if my ex signed and received into her bank account money from me, does that make any CSA claim invalid as she has received and accepted payment , therefore any further payment made now is on top of the one received more than 10 years ago.

I would rather kill myself than pay this again. I spoke to the CMS this week and basically was told that unless there was a mistake in their calculations then I am liable for this payment regardless of what was agreed between us. I do not have a good relationship with my ex even after 17 years and was told by the CMS that she made it clear she wanted what was supposedly owed to her.so no compromise can be made

I am at my wits end, I've not slept properly for months. it's now 1:45 am and I feel that being £10,000 in debt is going to push me over the edge. I left the marriage in debt and spent a long time getting out of it, only to be pushed back in by someone I left behind a long time ago...