Just curious - did you answer any of the calls?? If so, what did the caller say.
I'm only asking as I had something similar a while ago - kept getting phone calls in the early hours of the morning (I can't remember where the calls were from - might even have been UK).
Anyway I managed to catch one of the calls, so I answered it. The guy asked for someone I'd never heard of; I told him he'd got the wrong number and I was never bothered again.
It might just be a genuine mistake .... although it could also be a prank .... you won't know until you answer it (assuming you haven't answered it already).