Receiving a telephone cal from a debt collector is not a pleasant experience. Being hounded by someone attempting to collect a debt you do not owe is fraud. The Federal Trade Commission (FTC)  has recently brought charges against a Georgia based debt collection business that the FTC claims collected more than 3.4 million dollars in relation to non-existent debts.  They were also accused of using  collection tactics that violated the Fair Debt Collection Practices Act.  Charges were brought against Lamar Snow, Jahaan McDuffie and Glentis Wallace along with a number of collection companies they operated under various names.
Subject to strict federal laws, legitimate debt collectors are permitted to call debtors, however, the law prohibits them from threatening imprisonment for the failure to pay a debt and attempting to collect a debt the debt collector knows is bogus.
It can be difficult to know when someone calls attempting to collect a debt if indeed they are legitimate or not, so the best course of action if you receive such a call is to not discuss the debt with the person calling, but instead demand that they send you a written “validation notice” by regular mail which describes the debt they allege you owe and includes a listing of your rights under the Federal Fair Debt Collection Practices Act.  Never give personal information over the phone to anyone who calls you attempting to collect a debt.  You can never be sure who they are.  If you receive the validation notice and it appears to be legitimate, you may be better off contacting your creditor directly because the person who called you may not be representing the creditor, but may merely have information about the debt.