Well, if they were legitimate, they would mail you proof of debt/proof they can collect. They'd also have your address. Per the FDCPA, do not pay any caller who refuses to mail - do not accept email or fax - proof of debt/proof your caller has the legal right to collect said debt. Refusal to mail this documentation within five days of their first call is a violation of federal law.
Was called by a person who called himself Mike Bernstein with a call back number of 321-396-7800. He was looking for my son. I told him my son worked till 10PM and would not be home till after then. Mr. Bernstein then told me that he would have a warrant for my son's arrest served first thing in the morning and that my son would be in jail by noon. He was nasty, rude and mean. BEWARE! Call came from Miami FL. 786-453-0584.