Do you think that once someone is an ex they should not be communicating with your family?

My ex and I broke up. We have a 2 month old together. He wasn't the best boyfriend and that's why we broke up. Since we've broken up he keeps calling my family. Telling them things to make them feel sorry for him so that they can try and convince me to go back to him. I called my cousin yesterday and told her basically to stay out of my ex and I business. He calls her all the time and finds out info from her about me. I told her if she continues to communicate with him, I will not talk to her. I told her he's only manipulating her to get to me. She said I don't have the right to tell her who she can speak to. He's a master manipulator. He acts a certain way in front of everyone and they all fall for him. Do you think I was wrong for telling her this?