Trying to reason with these people will do you no good if they are calling looking for someone else that owes them money.The point of them calling you is to either have you give up the person they are looking for, or to get you to put pressure on the persone they are looking for to get them to pay up. You need to send them a cease and desist letter certified/return receipt. Look on line for a sample cease and desist letter to credit card collection agencies. There are plenty of them, and if you don't have a reference or case number, simply put 'Re: Your calls to XXX-XXX-XXXX' in the subject line. Put in the text of the letter that you do not have any outstanding debt, nor do you know anyone that has any outstanding debt. Once they get the letter, they can try to contact you one more time, then they have to stop.