Prank Caller 3

What is the word to describe this? Consistency? Persistence? Overly attached? Mentally unstable? Initially thought that it's 2 person. But it's actually or should I say possibly 3 person. Didn't know I blocked so many numbers. Anyway, it's getting annoying. Whether you are a telemarketer or just an irritating prank caller, you should know when to stop. Contemplating whether to get the telco to block it. Since blocking the number on the phone itself doesn't work. The calls still get through.