Debit order incorrectly drawn and no date on refund

I settled my FNB loan account. A debit order was then drawn. When I called in I was told that I need to wait for the debit order amount to reflect then call back again to request a refund. Surely if my account is on a zero balance a refund should be processed automatically... I then called in to request a refund 4 days ago and was told it would take 48 - 72 hours. 4 days later I have still not been refunded. When calling again today I was told there is a backlog and the refund will be done anytime after 72 hours - does that mean a week, a month a year????