Call the police, see what you can do. Document, document, document. I sent a guy to jail for threatening to burn my house down without ever setting foot in a courtroom (I video-recorded the call with my phone, called the police, emailed the file to the detective). In the state of Texas it is legal to record phone calls and other (face to face) conversations as long as one of the parties involved in the conversation knows it's being recorded. I've seen a $20 personal tape recorder and mic allow a father to take custody of a child from an abusive mother.

Also relatively inexpensive are cameras that you might use outside of your front door if your father is showing up in person. It can help you document how often he comes by. Many of them will even send you an email if there's motion and you can access the video feed via the internet or your smart phone.

All of this adds up to sometimes it's frustrating but if the police can't or won't do anything, you can help yourself. Pretty much any of this only does good if you then call the police. Stay safe!