go to the police, unless the police are involved your phone company cannot do anything about it.only the police ca request a phone tap so to speak
My daughter (15) was getting death threats from her ex b/f and as soon as we contacted the police the network company gave the number to the police (as i remember they wont give out details of the person to you) but they did pull her ex in and warn him. the only downfall is that if its a pay as you go phone and not registered then they have difficulty tracing who the phone belongs to. i hope you get it sorted as it drove us mad at the time.