What have some of you done to fight child maintenance when you've not agreed with it ?

We have ss more than 174 nights which categorised us in the 4th column of paying less than 100 and I could say we have him 50/50.However maintenance have to validate it to the other bio parent. Which they are denying and even lied to get it to increase.

Salary is also taken in consideration but you know when you're paying too much.