NEDBANK - WONT CANCEL A DEBIT ORDER AND KEEP TAKING MONEY

I paid off my sons student loan (***) 3 weeks ago and asked the lawyers over 2 moths ago to cancel the scheduled debit order (which was done by Nedbank) on my FNB account. They have for the 2nd month in a row continued to take the money off my FNB account. I called them and was put through to 5 different people, none of them could help, because THE ACCOUNT IS closed and paid in full # weeks ago. YET THEY CONTINUE TO DEBIT MY ACCOUNT AND REFUSE TO STOP THE DEBIT ORDER. I cannot stop the debit order because they created it and nor can FNB, to reverse it I have to pay FNB money. Nedbank is probably the most useless bank I have ever dealt with and I am going to take this to the ombudsman. I cant get my money back or cancel the debit order without clsoing my FNB account which I have had for more than 9 years.