FNB Authorised to debit customer account without confirmation

I would like to find out how FNB has the right to debit a customer account without confirmation with the customer?

My account was debited and when I spoke to Mpho from the complaints department, she confirmed that it shouldn't be like that especially if there is no arrangement.

I just spoke to Sibongile from the collections department and she says there is a contract that I have signed that says I agree that FNB will debit my account without authorization from me if I fail to pay my account. When I ask her to send me that contract, she puts me on hold, comes back and says I have sent it and wants to hang up but I ask her not to hang up and ask her another question. After a few minutes I see no email, she says, no I haven't sent it. I ask her to refund the money that was debited as I need to pay school fees, she puts me on hold, comes back and tells me that I can't get the refund because there is no arrangement on the account. I say why is it right for FNB to debit without my consent, she tells me that' sI made an agreement to pay the account monthly and now I am not and that FNB will debit my account whatever amount every month as long as I haven't made payment??

What a shock!

Please can someone confirm if this is correct.