control account

The list of balances is the list of balances in the receivable ledger. Interest charged on overdue accounts is interest charged to customers who pay late. We account for it by debiting the receivables ledger control account and crediting interest receivable account. (And, of course, we also debit the account of the customer who is being charged the interest)

What is the double entry for refund to customers?

Yet again, I deal with this in my lectures - I explain refunds (and the entry) in the lecture on control accounts. Dr Receivables Cr Cash