Amex Credit Card Complaint

Amex Credit card department,

Billing disputes Texas

I have a - prepaid credit card. I can only spend money that is available on the card. Although the balance on my card was - - American express approved a payment of approximately - $ making a negative balance on the card and are now forcing me to pay the balance. American Express can not explain how a charge of apporximately - $ was approved on a prepaid card which had - balance for over a year.