We had a telemarketer who had constantly kept calling, somewhat like harassing and it was a PRIVATE number. I mean these people were insane they would call throughout the night 1,2,3,4,5 in the morning I mean insane, but even if they aren't that insane in your case what you have to do is call your phone company and explain to them the situation they will view your calling history and see the caller as private they have the ability to see who it is however they can not release the information with you, what they can do is block the caller from calling or change your number. I know this is not that much of a help but this is the best they can probably do, I say give it a shot and see what happens, I truly do not know what posses these people.
Hope this HELPS!!!SOS!!!
Verizon, Phone Technician, Personal Expierence