FNB debit order system issue

Good day, I am in search of help in reporting fnb's online debit order system that is causing us as consumers to pay ridiculous banking charges due to their inability to manage their banking system. Every month I'm paying hundreds of Rands sometimes my account goes over minus R1200. Fnb starts debiting my account before my indicted debit dates every month and it results in my account going into minus every month. What's so disappointing is that the bank does not take any responsibility and I have to pay for their mistakes every month. I've been an FNB client for almost 20 years but I think it's time to move my salary from this bank because I cannot afford their mistakes anymore. Fnb please take responsibility for your mistakes, life is expensive.