Get a cheap answering machine that shows caller ID. If you don't recognize the number, do nothing while your machine takes the call. They hang up. After a few more tries, they stop calling. At least that's been my experience. Best $25 I ever spent.
I asked him if I could call him back. He gave me the number 1-800-690-3683. Said the company name was People Connect USA. Tried to keep me on the phone and convince me to do something but I apologized, said good-bye and hung up.