These are scam artists trying to get you to say yes on the phone so they can record it. Possibly maybe to jam you up with charges on your bank or phone bill.
I NEVER EVER answer my phone to unrecognized numbers. If its a legitimate call, they will leave a message. No message left tells me its telemarketer scum. At times I find it humorous that these low lifes continue to call. If more and more of the American people would not answer their phone to unrecognized numbers, these pieces of whale dung would go out of business. In the meantime, I simply let it go unanswered and block the number.