Scam robocall. Do not answer or attempt to engage the person if they should gain access to your phone, just hang up. Best not to answer calls from numbers you don't recognize.
>>> Obviously, the Do Not Call Registry is a joke. <<<
No, it's not. It's an actual device located in a temperature-controlled self-storage unit in Buffalo, NY. See http://800notes.com/Phone.aspx/1-888-349-8830#p761441779428157092
>>> I have stopped answering all unknown numbers. <<<
Well, good for you! That's what all the "regulars" here have been recommending for a long time!
Never underestimate the power of stupid people in large groups. (Boiler Rooms). What a bunch of morons. Now it's Betty Riggins and don't forget Roberto Ortiz. Now I understand why animals sometimes eat their young.