What to do if someone charged $2,500 to my credit card but the company can't find who did it and now they have a collection agency that wants $2,500 in full payment?
If you can prove that it wasn't you or anyone you authorized, then even if they can't find the person who did it, you should not be liable. Therefore, you should focus on proving that you were not physically where the charge was made, or that you had reported your card as stolen, etc. If they will not believe you and voluntarily drop the attempt to collect, you will have to defend yourself in court on this basis, if they sue. The key point is: you can't be held liable for charges you did not directly or indirectly (such as by letting someone else use your charge card) incur.