All debit card payments are processed as credit transactions. They are finalized when orders are shipped. That is, no payment will be transferred to us until then. However, when you placed your order, the issuer of your credit card will process a credit authorization for the amount of your purchase.
Credit authorization is a step in which the card issuer grants the store an authorization to process the payment. Once they authorized it, the amount will be blocked for the payment until it is finalized. Normally, once the payment is finalized, the authorized amount disappears from the online account information, and instead, the actual payment appears on the credit billing statement. However, it may take up to 6 weeks or so until the authorized amount disappears, entirely depending on how soon your bank updates the information. In that case, it may have an appearance that you were billed twice, but you are billed only for the amount that appears on the billing statement.
Whenever you add items to any existing order or move one item to another, a credit authorization will be processed for the new total amount. The previously authorized amount will be voided immediately when the modification is made, but it may take up to several weeks before the voiding of credit authorization is reflected in your online account information.