What can I do to stop my stalker?

My fiancee's ex girlfriend from over a year ago keeps finding our number and having people call at all hours threatening me. We have changed our number several times.And even gone without a phone for months. Also when ever I happen to see one of her friends out at the store or whatever, they yell obscenities at me in front of my kids. I want to get some sort of harrment order put on her and her friends. But don't have the money and do not know her phone number or address were she stays or much info on her and her friends. I've tried to ignore this, have contacted her mother where she stays and the girl acts like I am the one who is stalking her. She is 23 years old and on probation, can I find or tell her officer? So I've tried to be nice. The police tell me that I need her address, but she runs around all over town. What can I do?