How can HMRC and the CSA believe these people?

In 07/08 I started to receive £350pm for my 2 children,regular late payments as the vile ex was abroad sunning himself.So after around 11 months he decided to get a new job (company director) paid himself in dividends laughed in my face whilst telling me his accountant has “sorted his books” resulting in my kids being entitled too £1.77pw for both!!!

So I told csa to shove it