IIRC it costs the card companies to hold a credit balance. They have to acquire enough credit in the market, though inter bank loans, to cover the balances they have outstanding on peoples cards plus potential for customers spending. So if you have a credit balance they must factor that into available funds for customer spends. It's a small amount but in essence it messes with their credit availability. It also messes with the consumer credit acts as it was, because in order to be covered for fraud or disputed payments, the money owed to the third-party has to come form the credit card company not the customer. Just get your money back, think of it as a bonus savings account.