Moving my account to another bank

I am so disappointed with FNB, who is unable to assist me with the debit order dispute. I cancelled the mandate with the service provider but my account keeps being debited. I requested FNB last month to stop the debit order, and I was advised it has been stopped. To my surprise the month the debit order went through and the consultant told me they are unable to stop and reverse the debit order on their system meaning the money will keep going off on my account. I do not understand how as my bank are not able to assist me with this. I am left with no choice but close that bank account and go and bank with another bank because if I remain with FNB my money will be finished and I will not get any help from them.