Debit order dispute.

I am very disappointed with the service under debit orders for FNB. I have been their customer for more than 10 years . I have requested to dispute strange debit orders from my account since Monday 25th Jan 2021 till today with no luck, despite numerous calls and chat through their app. FNB does not do the dispute telephonically is only via the app or cellphone banking off which their processes and systems are not effective and efficient and also time and money consuming . every time when i try to chat to the banker they write that "thank you for your chat. We have had no further response from you, please contact us at a convenient time, when you can chat." As a premium banker I am struggling to get the best service from this bank.