Evidence for csa

My ex has 'evidenced' to csa that he earns less than 20k but during our divorce finances he sent me his bank statements and it shows he earns over 100k.
He is lying to Hmrc and in turn the csa.
what should I do?

CSA haven’t existed for some years and I don’t think there are any cases still open so I assume you mean CMS?

CMS don’t take income evidence directly but get their figures from HMRC. They will then take into account pension contributions made directly so your ex may have increased pension contributions significantly.

If your ex is self employed they may also take some of their pay in dividends. Perhaps they have chosen not to do so last tax year to lower their taxable income?

When do the payslips relate to and were all the figures personal income or was the account used for business use?

Yes apologies I meant cms.

He gets paid directly into his personal bank. It was a company with its own bank but he dissolved that last year and continued the business from his own bank. (For the benefit of the divorce is why he did this)

He doesn’t pay tax to Hmrc as he tells them he doesn’t earn enough. (So basically it’s tax fraud too)

Why wouldn’t cms accept his bank statements?

If you think there is tax fraud report it to HMRC.

You could apply to CMS for a variation of you think there is other income to take into account.