I am being de*****ed by my own bank!

I have had such an awful experience with FNB. I have banked with them for some years and last month contacted them regarding an unauthorized debit on their feaud app. No response. Suddenly they are debiting my account with unauthorized amounts wgen my balace is nil and then charging 50% interest also debited from my account . I never authorized an overdraft, neither do I want one. I now have a debit of oved R700. for nothing I have or have authorized. 1 week ago I spoke to a consultant andxwas informed that I would receive a reply within 24 hours. I am still waiting !! This is totally unacceptable. By the way you cannot close an account ina negative balance. Interest continues to accrue . Disgusting attutude and service.