Debit order for R99

A debit order of R99 is going off my account that I did not approve. When I ask the support staff at FNB to stop the debit order they put me to a different person ever time. Even though there is no money in my account the debit order bounce but it has caused bank charges. They want me to stop a debit order I did not sign. Isn't it the banks duty to stop debit orders. The staff gets a fat salary for not working.