What can I do if my ex and my father are now making decisions about my daughter without notifying me?

My ex is always coming by my house, and telling my father that I don’t pay child support. She says that I don’t call and talk to my daughter. She comes by my home and yells that I do not pay child support, and she has my father believing her which is causing us to argue. I recently filed to modify my child support and to get full custody of my daughter. She is always calling my father with new lies.