FNB refuses to reverse a debit order that went through

I was debited on the 27th of November, on this same day I contacted FNB to tell them I would like that debit reversed. However, the debit order didn't reflect on their side as they are experiencing technical problems. I called again today, and same problem. I was made to hold on the line for close to 20 minutes to be assisted only to be told that I can't be helped. In the meantime the 48 hours in which I am supposed to reverse the debit order is soon to lapse. I also tried to message their online bankers on my App and this person said the debit order can not be reversed as I have an agreement with the people debiting my account, what ******* response is that! I am instructing my bank to reverse a debit order, and they are telling me I have an obligation to the people that are debiting my account, so whose interests do they put first, mine as their customer or the people debiting my account. My money is supposed to be safe at FNB, and yes I did give permission for my account to be debited, however I told the people to no longer debit my account for personal reasons. Instead of FNB honouring a client's requests, they are gambling with my money! I want this transaction reversed!!! Or else I am going to take my business to an alternative bank.