This is supposedly a debt collector. They try to scam people by trying to intimidate them into paying other peoples bills. Illegal.
Contrary to what the advice on this page states below, the do not call list only works with legitimate companies who choose to comply with the law. If they dont comply with the law and you report them as I have countless times, nothing is ever done about it anyway.
File a report with your local police.
 Mar 12th, 2013