Hi again Fido:
I've just read the bit about what the WPC told you. However, such advice may not solve your problem and it smacks to me of the WPC trying to "'cuff" this. That's Police jargon for wriggling out of doing something about it, i.e. sow a few seeds of doubt in a person's mind instead of taking some positive form of action.
Plus, her remarks about going round to the lad's house "for a chat" are quite frankly laughable. If this lad is 14/15, he's perfectly capable of being responsible for his actions (unless he has a mental incapacity). And chatting to him would simply make him aware of the complaint and put him on his guard.
Didn't she mention that, with BT's help, a trace can be put on your phone for, say, a week, and all calls would be monitored during that time and the nuisance ones would be identified and the culprit could be prosecuted?. If she didn't mention this, I would suggest that she IS trying to "cuff" it.
Ultimately your choice, but you don't seem happy from what you've said, and I don't blame you. Doing nothing will not resolve this.