Dickhead of ex

So not sure if on right group but basically me and my ex broke up last January it was clean break up i just didn’t love him anymore he obviously was upset but said you know we can be friends still got a young son together be there for each other go out on family days out so not much of a change for our son, but then he met a new girl and there where everything changed. I met someone new too. His girlfriend was messaging me saying she my sons mum she will get him taken away everyone will know what a awful mum I am my son will soon know. My ex let her say this all to me to my face and over message. My ex is being controlling saying he wants to see his son more I don’t let him see his son when i do, he can whenever he wants but I do want it to be 50/50 so w both get time with our son. His girlfriend recently made complaint to social services to get my son taken away didn’t work. My ex calls me disgusting a bitch not once said ima good mum. Said I’m a nobody no one loves or cares about me. We are currently seeing mediation but that doesn’t seem to be getting anywhere my ex won’t cooperate won’t meet in middle he wanted all or nothing basically. Anyone gone through similar thing? Any tips what can I do? I try to talk to my ex less as possible wish I could delete his contact but have to keep it for our son. If I ignore him I’m bad person I’m controlling im childish I’m not being civil and being a mature parent as I’m ignoring him but when I do talk to him I’m in wrong I’m controlling his girlfriend always interferes. Please any tips or help? Thanks