If you get these call start calling your phone company. If it is a cell you can sent the call to your voice mail. I have a ringtone for all the 100 that have call that will not even ring, just send them to voice mail of which there is no voice message.
Don't answer calls from unknown number...otherwise they know they can get a person. If it's important ...they'll leave a message. Got a call from this number today...didn't answer and no message. Don't expect to here from them again.