Can I take the CSA to court?

We have been clients for nearly 18 years. The parent with care opened a private case and has closed it 3 times. We had a letter back in August claiming we owed some £4k (this mainly accrues when she closed the case and reopened it under the new system of 20% of salary no matter what! The CSA “lost”8 payments of £65 totalling some £800!!!

I wrote to them for them to check it and guess what? 3 months later a letter stating we owe £6800???????? I think they have calculated the amounts when the case was closed and added them on. I have all the paperwork since day 1 thank God including closure letters which have sent to them.

I am waiting now to hear back. Will I get an apology? Can I take them to court for this if they dont admit a mistake. We have no contact with the child at all The CSA’s involvement has caused nothing but hassle mainly to the parent with care as she is not interested in the childs relationship with her DAD just the money which she doesnt really need.