KennyE wrote:my first instict is to put my fist through his f..... head
This is almost my first instinct in every situation, and let me tell you, acting on it has gotten me in a lot of trouble many different times. Don't confront him. Don't try to track him down on your own. Don't threaten him back. Don't do anything that could be seen as illegal or inflammatory. Let the police handle him.
Next time this guy calls your daughter, contact the police right away, just in case there is some issue with time and tracing the call. Unless they've already been able to trace it. And you're right, being forced to change the number is very hard to accept as the best option. But if it really comes down to it, keeping this guy and other guys he knows from calling your daughter in the future should also be a priority. I'd say contact the police, change the number, and hope he's dealt with swiftly. Of course, the final decision is up to you and how you feel about the situation.