We split 9 yrs ago. For that entire time he has paid £300 a month.
He is self employed so I never went to the CSA as when we got divorced he declared he was earning £800 a month 
He is remarried and they have two businesses - I suspect both in his wife's name and one of his businesses he can be paid in cash - often.
DS is 18 and has left school and has a job and pays his way.
DD is 16 and ex has this month halved the maintenance to £150 a week. Her bus fair and A'level cookery in themselves cost me £30 a week.
What can I do (if anything) I know if I take him to the CSA I am pretty sure he is paying me in line with what he is declaring tax wise.
He went on four two week foriegn holidays last year - it makes me so 
Is there anything I can do?