stuck

so my baby father and I agreed not to talk to the opposite sex in our relationship that didn't last he hangs out with a girl I don't like I told him to delete her number and stop having her knock on my door he said ok but when my ex boyfriend messaged me on fb to see how I was doing and to check on the kids he got mad and went and messages his ex now by the way don't forget bout the girl I don't like he was texting her and didn't tell me he claims that he told her to stop knocking on my door but she still knocks so it's 10pm and he has been upstairs with her since 3pm with her his friend and him what should I say to him