When an online order has been placed, Card providers allocate the required funds for that order. This means that the transaction amount is unavailable to you and reserved for the order.
During the time of processing, if any item/s is out of stock or there is a price decrease, we won't charge you the entire transaction amount and the final payment processed, would be different. We'll only complete the payment process once we know the order can be completed. Due to this, there could be two entries on the statement (one for authorisation and one for payment) but the amount is only deducted once, which can be verified by checking the available Card balance.
The extra funds, if any, will be back in your account by a period determined by your bank (usually 1 to 10 business days).