Unfortunately, debt collection agencies will pass unpaid debts onto a new Debt Collection agency for a profit. When this is done, situations like yours will occur on a continuous basis. Under the Fair Debt Collection Practices Act (FDCPA) if a debt collector/agency cannot verify that a particular debt belongs to you within a thirty day period, they must by law cease collection efforts unless they are able to verify. Not certain what the letter you use asking for verification states, but it must state the relevant law, and strictly forbid the debt collection agency from collecting on the debt or passing the debt onto other agencies until it is verified. If this collection effort has shown negatively on your consumer credit report, I would also contact the credit bureau's and inform them of your efforts to have this debt verified, and to allow the credit bureau's to dispute this information. If after 45 days, the collection agencies fails to respond to the credit bureau investigation, or fails to verify that the information on your credit report is accurate, then the credit bureau must delete this negative information from your credit report as well.