This is a debt collection agency that traffics in "zombie" debt (debts that have passed the statute of limitations).  If they can find the debtor and convince him or her to pay even a token amount the debt reactivates.  They use old phone numbers and will call DAILY even after being told the person they are trying to locate no longer has that phone number.  These people are unrelenting and rude.  Telling them to stop calling is pointless--best to ignore them even though once they have your phone number they will NEVER stop calling.