I am going through this right now. Overpayed AMEX CC for several thousands and my CC has been automatically blocked by the system. No one can override it or modify it. The block will last until the end of the monthly cycle. Somehow the block took about 24 hs to kick in and in that time I was able to spend to half my CL but I also send several payments by mail foreseing they were going to arrive different days and I was able to put more spending but... now it's blocked so I will be with negative balance again and not only that, I will begin the new cycle with big negative balance. I will try to request a check when the payment take place but I don't know if it can be done and how quickly. I'll keep updated