UAUTHORISED DEBIT ORDER

Hi: I have a problem with FNB I am their new customer for two months i have just open a current account with them.i was expecting good service from them.I know that i owe Fnb the credit card which i have **** an arrengement to pay them althou sometimes i am late with my payment.On the 25/08/2017 Fnb authorise a debit order of R3832.48which i never allowed or agreed to it.I went to Fnb trying to reverse the money which was too much I was told they could not do it because its one of their lawyers who derbited my money.I was not informed as a account holder that they will do such thing and the amount that they took it is way too much of which i could not pay the school fees and the transport for my child.I have living expences and dept beside them what do they expect me to survive with for the whole month?yes i owe them and i am willing to make arrengement to continue paying their account.I even tried to call their customer care few times but my call was not answered.Please hello peter help me.