Hi-C's

I made reservations for 2 rooms at the hotel, and called prior to my trip to adjust the arrival date. I wasn't given a confirmation # for the change so my office called again to confirm & was told everything was ok. I arrived late, hotel was closed, but keys were in a mailbox. In the a.m., I rec'd a note to come to the office to settle up. Reception asked if they should use the same card on file, I said yes. They handed me the slip to sign, and upon checking out of the hotel, I rec'd the full receipt which included 1 extra room night for both of my rooms. A total over payment of $251.86. I am contesting the payment through my credit card company but having issues because I signed the slip.