Just ignore him. Everytime he calls, just ignore it and send him a message along the lines of, "Sorry, I'm busy."
For Facebook, you can appear offline to certain friends. You can just use the same line, "Sorry dude, I've been real busy."
I have a certainly grace period I give to people where I give them a chance. If they're annoying or have attributes I hate, I slowly start keeping my distance. If that doesn't work, I start acting like a cunt to them. But if they're online, it's easy peasy to ignore them.
In my opinion, if this kid isn't in certain social circles you frequent or basically you don't or aren't going to see him around, then I'd just block him.