auth user on credit card

Arizona....Hi. A family member, aprox. 4 yrs ago placed me on their credit card as an auth user. This credit card has now gone into default for the past two years. The credit card company keeps calling me, the auth user, stating they have me on the card as a joint cardholder, and thus, responsible for the balance. I have never had a card with this bank, nor have I ever benefited from this card. (I am a fraud Inv. for a major credit card company, and I see this situation many times, and I handle and investigate the complaints and legally my company has to investigate any fraud or complaint made.. but I can not understand why this company in question will not investigate their error by placing me as a joint, instead of a/b...) I have never signed anything stating I wished to be a joint holder, nor have I ever verbally advised them to place me on as a joint holder. They have now forwarded this acct to legal representation, and I constantly receive collection calls for this family members balance. And I have no idea where this family member is, no contact with this person for several years. This isnt a case of fraud by my family member adding my name as a joint, I feel the company added my name in error as joint user. What can I do to get my name removed or to get them to at least investigate the situation? I have written to the company, advised the attys involved, yet nothing seems to be done. any suggestions would be greatly appreciated. ...I have requested they provide my signature, a letter or a sales receipt with my name/signature, two years later they still have not provided anything. Thank You...

[bigun]

Send them a letter {RRR} demanding proof that the debt is your responsibility. If they don't respond within 30 days, sue them.