FNB refusing us to reverse debit orders

Can someone explain why one can't reverse and stop debit orders over the amount of 200. You call FNB and they refer you to the app, online banking or cellphone banking but none of those have the functionality to dispute the debit order. Went to the Branch and they tell you they don't reverse debit orders and they get you a phone to call FNB but when you call they refer you the APP again. Need my debit order reversed. Switching to another bank after this. Their Premier Bankers are also not helpful at all