Unpaid refund by nedbank

I have a home loan with nedbank. I loaded a stop order with my employer then after a year I decided to cancel the stop order and load a debit order with the bank. It took some months for my employer to cancel the stop order resulting in a double payment by both my employer and the bank. I had to call the bank to reverse and refund one payment. Every time I call I am told the refund will be paid within 48 hours and that does not happen. I don't know what more should I do for the money to be refunded.