Won't pay money back that was overpaid in settling account

My husband phoned and asked for a settlement letter on the 26 April 2018 after transferred for about 20 min on which the lady couln't help him. Nedbank who was settling his account tried to phone and was transferred from one to another. On the 30 April he phoned again and being transferred everywhere they told him he must sent the settlement letter from Nedbank to pay the money back that was paid in too much. After sending and sending it until he hold on till they confirmed they've received it they say they will pay it back in 5- 10 working days. A month later nothing happened after numerous phone calls and time holding being transferred and being told Andrea don't work there or is on leave she finally told him he should have asked for a settlement letter because he had paid the outstanding amount and they can not pay it back ??????WHAT !!!!!!!!. Asking to speak to manager it is this way and that way . WHERE IS THE MONEY YOU STILL OWE US ?????????? They are very fast to give you loans until they owe you. Never in our lives again