The Account Credits page displays all of the credits associated with your billing account. Any additional payment toward unused or canceled service is credited/refunded to your account and reflected in the "Account Credits" page under Billing.
These credits can be used to buy new services or place a new order. Or you can use this amount to pay your invoices as well. At the invoice payment time, choose the "Apply Credit" option under Payment Method to use your available credit balance.
Utilize the search feature to locate credit information by filtering according to the Issuance date, Credit ID, Description, etc.