Balance paid in full no proof given

On the 2nd of September. I paid the balance on my account. When I did a follow up on the 9th they said the payment doesn't not reflect. I even attached proof of payment. All I need is paid up letter confirming that the account is closed. They are so quick to remind you about when you have outstanding balance. Yet when you pay it takes 7 days and more for a payment to reflect. Please just give me my paid up letter and close my account immediately.