Right i have my ipad on now so i can tell you exactly what hes up to.
He is counter claiming. This means that he is claiming he doesnt live at the address his other children live at and that he pays child maintenance for them. The reason he is doing this is...
You are going to very soon want child maintenance yourself so when you go through the cms they will calculate what he should pay based on children living with you and children living with his current partner. If he declares he is living with his current partner then the cms only allow a very small deduction for children he lives with. I think its £7 a week deduction.
However if he doesnt live with any children then you and the other mum will receive an equal amount of child maintenance.
For example you have 3 children with him and he has 3 children with her. Hes been calculated at the full child maintenance of £60 a week to you. Now if he lives with her and their 3 children he will get a reduction of £7 ish so the amount payable to you would be £53.
However if he doesnt live with any children and he has children with different mums then the money is shared out. So if you have 3 children each then you will get £30 and she will get £30.
This means hes much better off financially as that £30 is going into their household pot that he claims he isnt living at.
There is a group on fb called child maintenance rip offs original and they advise that they do this counter claim on there.
I hope im making sense here, its hard to explain in writing.