Poor business conduct

My overdraft amount was reduced by R500 without my consent. The monthly fee that I pay was increased resulting in my business account being overdrawn. There had been someone from FNB business desk who had been calling me asking if they could reduce the overdraft by R500 every month but I did not agree telling them that I would think about it only to find my account overdrawn by R500. All I want is for the R 500 to be reversed and to continue paying my normal overdraft financing costs. My business account number is ***.