The court is not really going to be interested in what happened months or years ago, they will only want to know what’s happened since the date of your claim.
I think a good starting point would be to start at the date of the claim of CMS. You are going to waste your own and court time trying to argue about your primary carer role before the CMS claim. They don’t care about this you must drop it.
Lots of people have tried to help you understand that the CMS website doesn’t have any nuances, so what happened is that they allowed you in good faith to make a claim based on information you provided to them that you did more care and had more responsibility than he does, plus you didn’t know his earnings. They made a claim based on what you said, and he made a counter claim based on his view.
The concern is that you may have given them fraudulent information.. he doesn’t agree with you as he can prove he had your kids MORE, which you have admitted to so your ex was given his own opportunity to counter claim against the untruth that you claim to be the primary carer. It’s his right to do that, and when he did win the child benefit this is pretty clear cut.
The case is going to be expecting you to prove you are primary carer, but your proof is very flimsy and easily disputed and you have very little chance of winning. He had them more nights than you and the admin seems negligible. This is why people are suggesting you call a truce and end this now because you could actually get into more debt and issues fighting him is that what you want?
you need legal rep it’s very obvious you don’t have any