I’m struggling to stay afloat while my ex lives a life of luxury

My ex patrner was told to pay £90 a week when we seperated 6 years ago. He was on a good wage but then suddenly left his job to be a director of his new business.

For the last 3 years he has told the csa he only earns £120 a week and therefore pays less than £15 a week. It is completely obvious he doesnt earn £120 a week. He lives in a brand new 4 bedroom house, him and his parnter drive around in brand new BMWs and take exotic holidays 4 times a year.

Ive told the csa but they say its up to me to prove that he is lying or to ring the Tax man. They say his partner might be paying for all these things. Surely it is down to the CSA to look into this but they wont! Hes laughing at me because he finds it hilarious that i am struggling to keep my head above water while he lives a life of luxury. He has no other children and i know he would never have left a well paid job to earn £120 a week. What can i do???