How much CSA is fair for one child?

Cannot stand the CSA and it’s beyond me how the people who work for them can get any job satisfaction. I currently pay £58 a week through the CSA for my son, I have never missed a payment in his 9 years.

Now through hard work and wanting to better myself I have worked my way to a better position within my work, ex found out I got promotion and has now asked for a review, will now be paying £88 a week to fund her social life as she gets everyone and anyone to watch him so she can get out every weekend.

Realistically how much is a fair amount for 1 kid ? I went to her and asked her to be fair and I would pay £65 a week directly into her bank, yeah you can guess what the answer was. Feel like handing my notice in and give her feck all, but not fair on my son, i’ll just need to take being shafted yet again.