I know it's an inconvenience, but turn off your answering machine. I turned mine off about 2 years ago , and these calls have stopped coming at a rate of about 90 percent. Also, don't answer your phone if you don't recognize the area code, or if it's a blocked id , or an out of area call.if you answer, they will continue to call!
Alternate energy supplier doing solicitation calls. I asked to be removed from their call list but that didn't help.
I receive about 3 to 4 of these calls per week - mostly with PA area codes.
I guess I have to block a whole new set of numbers.