When you place an order, we contact your bank for a purchase authorization to verify your [card / reward points / checking account] but don't actually charge you until the order ships. Some banks may hold funds in your account for these authorizations even if the order is canceled. Orders from our Marketplace sellers may be charged at the time of purchase.
You'll need to contact your bank for assistance. They can tell you why funds on your account may be unavailable and clarify how long they hold payment authorizations for online orders.