My ex won’t help and the CSA aren’t interested

My ex partner has our daughter to sign up for full time education and she leaves after a few weeks Ishe has done this for last three years I have informed the csa and they told me that I still have to pay because she claiming child benefit my ex won’t inform the child benefit agency of the changes and the csa are not interested every time I speak to them I keep getting told something different also my daughter is working.

CSA also told me that my ex won’t speak or reply to there letters when I said don’t you find that strange they told me she still claiming child benefit I finding this really frustrating any help would be appreciated