We get emails like this all the time and reply with something like this:
> I apologize for the confusion. Amazon Payments is responsible for all aspects of collecting payment for your orders on Amazon.com. As a third-party seller, we are unable to see any information regarding the transaction other than the date and amount paid. If you believe there was an error in charging your account, the best way to resolve your concerns is to call Amazon Customer Service toll-free at 1 (888) 280-4331. They will be able to look into the details of your transaction and make any necessary adjustments.