Unauthorised debit order allowed to go through

I have constantly rejected a debit order mandate sent to me amounting to around R2600. I rejected it a lot of times but somehow it still went through and reversing the amount seems like a tedious process. Reversing a debit order on the app is almost impossible or takes awfully too long! Please assist me to reverse this debit order immediately and release the funds back into my account. It is an ******** transaction!