Unauthorized debit orders 5 days apart

FNB approves debit orders on my account that I did not authorize. These ******** change reference numbers and debit on those dates15,20,25,31. The amounts changes from R96,R99 &. R109. The change referenced. They are in Durban. I phoned one of the number I got from their debit date confirmation and it is always busy. Every time the debit order went of, FNB sends me the message to reverse it. I pay for all these transactions. Currently I am not employed. If FNB can explain to me how does debit order works. Am I not supposed to sign documents to authorize it ? Did FNB get such documentation signed by me perhaps ? I need those debit order documents to be sent to me. Don’t tell me you don’t have because it means clients account are not safe with you. ********** are just dishing out. You are just approving. I have never had any of those debits or any debit order for those date. It has always been the last day of the month. I have been reversing these more than 5 times in a month. I have proofs of these notifications. FNB please explain you debit order process. I trust you with my money not to let ******** take it for who knows what. I am hating FNB and for now I will not recommend it to anyone. I await you response.