Unauthorized debit orders

Last month I had an unauthorized debit order on my account, I called FNB to investigate this for me as I had no idea who the Creditor was. I was promised that someone would call be before end of 7 days, as they usually say this but nothing happens. This month I have another unauthorized debit order. I feel it is a waste of my time and money calling FNB as they do not take me serious. I am getting fed up with FNB's poor customer service. If nothing is done about these monthly debit orders, I am so taking my business elsewhere, as they no longer serve their purpose on my account.