My ex hadn’t been paying the mortgage on our house and it’s messed up my CSA payments

I had a arrangement to pay my x £30 pounds a week and then when i got my house back off her she had not been paying the mortgage. So she said to pay her £20 a week to pay off the arrears and then in November last year, she told the CSA that she had not had any money of me from November last year.

The only time I knew about it was when they started to take £96.18 a week out of my wage this year. When I rang them up about it all I got was it is not they problem and then they said send all the paper work in to prove that I have been paying, which I have done 2 weeks ago and still not heard from them. It looks like I will have to ring them which cost a fortune to ring on a mobile and when I told them that she had agreed to the money of £30 then £20 they just don’t care that I don’t have any money to pay my bills and to live off. If it carry’s on I will have to give up work as I can not afford to work and live