unknown number, multiple calls

seems that all these numbers go around and around, get one number for a couple weeks/months, then another one starts up. Newest one is this one.....  GRRRR

wtf? i missed two calls from this person today. I did NOT know this number.

Every night, same phone call. Leaves no message. You would think that after the umptenth time and our unresponsiveness, that they would give up.

My friend has taken a run kid the mill referee whistle and answered the call with as loud as he possibly could. So far, no repeat calls. Not sure if the are any legal implications for these actions, but so far, he's gotten he result he wanted.