I don't answer calls from numbers I don't recognize. I have a message on my answering machine to that effect. It's that simple. Every so often I go through the list and do research on them. Any that may be calling repeatedly may get a nasty surprise.
IT'S THAT SIMPLE. have a message on your answer machine that states you are not answering calls you don't recognize and in order to talk to us, leave a message and a number if we don't pick up.
Would not stop talking when I politely asked to interrupt. Would only speak with canned responses. Refused to acknowledge my request to not call back. When I asked him to acknowledge my request for the final time, he said "I appreciate your request to call back at a later time" and hung up the phone.