Poor service

There is an amount being deducted off my account every month via debit order. I told FNB I do not authorize this to come off my account. They told me I must go and deal with the company that is deducting the debit order. They said they cannot stop it all they can do is reverse it every month after charging me a reversal fee every month. This is rediculous, as a bank you are supposed to protect me against unauthorized debit orders leaving my account.