Unauthorised Debit Order Reversal

I have a debit order which pertains to a contract that ended/cancelled. I contact the relevant financial advisor who advised me to ask my bank to reverse the debit order. My issue is the following: 1. When you contact via the FNB App (Secure Chat) their automated system reroutes you to the self service to reverse the debit order yourself. However the self service only works for amount of R200 or less, and you cannot reverse any debit order above that amount. I have tried on several occassions, and the app tells me that the amount cannot be disputed or stopped? 2. I called the FNB Gold Suite for assistance, and the automated system just takes me back to the app with a link to reverse the transaction via self service and none of these amounts can be reversible? 3. I was advised by FNB before that there are debit orders that can't be reversed which I find rather ridiculous which gives power to these companies to willy-nilly deduct money from our accounts?

I need assistance in reversing a debit(s) asap and stop wasting my time by referring me to useless automated systems which do not help me! I am unhappy with FNB and service received thus far, it seems as though each week I must complain about poor service received!