First and foremost, you are never responsible for charges made to a credit card without your knowledge. You should request a copy of the statement(s) in question to be sent to your attention. Upon review, if the charges are fraudulent, advise the bank and they will put them into a dispute file. You will likely need to complete some paperwork and the merchants will have to pull receipts with signatures authorizing the charges. During this time, disputed charges do not incur interest or penalties. Regarding not being a co-signor, you will need to ask the bank for a copy of the original credit card application where you would have originally opted-in as a co-signor. If they are not able to provide this, legally you cannot be held liable for these charges. Good luck!