My child dad

Opinions please. Me and my child's father have been split up about.4 year for the first 3 year he didn't pay maintence then I put a claim in for him to pay it. Him and his family was then giving me abuse saying I'm a money grabbing bitch! Everytine he payed it I got texts of abuse and he had him a lot more so he didn't have to pay not only that he's says my new boyfriend which is amazing with my son has more money than him so by rights he should have to pay for our child. Now he doesn't pay it he doesn't see half as much as he should and is more interested in seeing his new girlfriend and spending time with her what do I do?