Sorry if this is posted in the wrong place, but I can't sleep and could do with some advice.
So here goes. I put in a claim to CMS after I split with my ex. I heard nothing back from them due to lockdown, and he refused to pay anything either. He claims he shouldn't have to. They recent got back in touch to say they was going to look into the case and would try to get in touch with the ex. They also said it would be back dated from the start of April.
On Friday, I received my letter stating how much he has to pay etc and that if he doesn't, I can ring and they will use the collect and pay service as well as add an extra 20% on this. They also added an extra amount as it has been backdated.
The DC were with ex this weekend and I was due to pick them up yesterday so I thought I'd speak to him then. However, he said they wanted to stay and he would drop them off in the morning before school. I said that's fine, it's very rare he has the kids an extra day but also I don't begrudge my children that extra night with their dad. Anyway, that's a bit beside the point.
I text him to say we needed to talk about said letter and asked if we could do it in person as words can come across differently through text. He didn't want to do that, he then proceeded to text me that he refuses to pay it and that they can't do anything about it. It got quite nasty on his end. He also threatened court for the umpteenth time.
I told him there's nothing I can do, I apologised that the amount is so high and reiterated that it is for the children and it is the minimum that they should get.
My ex is extremely money oriented and I can tell that this has touched a nerve massively. He's now refusing to give me the deposit for the house. Told me he'll tell the court anything they need to know because I'm a money grabber and cannot provide for myself 
Although I paid for EVERYTHING when we were together.
Back to the point, if he takes me to court I assume that they're just going to say that he has to pay it anyway. Will they just laugh at him? Shall I ring CMS and say that he's being uncooperative? I don't technically need the money, but the children are entitled to it so why shouldn't he pay.
Oh I almost forgot, he's kept his receipts of what he's paid for the kids so I need to be worried. His weekly 2 day shopping bill absolutely overrides the £500 maintenance he's supposed to pay. Did I mention he's an idiot?😂
Thank you for reading!