Court ordered maintenance - non payment

Hello, I'm hoping for some advice on how to go about taking my ex-husband back to court for non-payment. He paid the full amount of £1,350 once, then halved it, then continued to pay less and less to the point where he was blackmailing me regarding the children for £100 amounts as and when he felt like it.
As you've probably guessed, it was an abusive marriage and at this point there was still police involvement, I had 4 children to bring up, one of whom had severe epilepsy, so I stopped answering his demands and he stopped giving me any money at all. I lost my home which the court had awarded me as I couldn't pay the mortgage and he then declared himself bankrupt.
The order is now 10 years old, my youngest daughter is just about to leave school and start college, so it should still be being paid.
I have spent years trying to get away from him but he always finds me. Over the past year, things had been civil between us, but now he has started being abusive again and I have had enough. I am going to take a stand, this has to stop and we are living on benefits while he cruises the far East in first class etc and has a minimum of 4 holidays a year.
How do I go about this? I will obviously be self representing as I had to do through the divorce, so I need all the facts before I do this.
Sorry for the long post.

I'm pretty sure you can apply for him to pay your court costs because he isn't sticking to the agreement.

Most courts have law students available for support when you self-represent. They can't give legal advice but may be able to find out for you.