Two different records, and people look for hourly charges in the wrong one.
Invoices
An invoice is money coming in: a credit top-up, a deposit, a prepaid month or year, a bandwidth block. Paying one posts a matching credit entry to the ledger. Invoices are listed under Billing and each has a receipt page you can print or hand to accounts payable.
Each paid invoice posts credit once. Refreshing a receipt or receiving a delayed payment confirmation cannot add the same money a second time.
The ledger
The ledger is every movement of the balance, in both directions: deposits and bonuses up, hourly server and floating IP charges, bandwidth overage and API overage down. Hourly usage does not generate an invoice, so if you are looking for "where did my credit go", the ledger and each server's Metrics tab are the place.
Credits and corrections
If support credits your account, that is a new ledger entry, never an edit to an old one. You can see it, with the before and after balance, in the same history.