Why are you charging my credit card for a negative balance?
Our payment system will not generate settlement reports for seller accounts with a negative account balance. Therefore, Amazon charges your credit card the amount of any negative balance at the end of each billing cycle. This allows our payments system to post regular settlement reports detailing your recent account history even if you had a negative balance at the end of the settlement period.
A number of factors can contribute to a negative balance including:
product refunds, especially if you issue a refund for a product for which you have already received payment. Note that charges would occur in the currency of the Amazon Marketplace. Hence Amazon.co.uk will charge in GBP, which might result in a charge of exchange fees by your bank.