FNB Credit *****

Ref Secm *** good day,here is my ref no.I still haven't received my email were Fnb said the case is refuted.On the 1 April I made the payment for R11,99 to post office.Fnb send me OTP. I did as normal and insert the OTP. I thought I am paying for the R11,99 and the next moment two amounts went off R1987.92 and R996.93. Why did Fnb send a OTP to approve the transaction and not warn me of a ****?Surely they have firewalls in place for these ***** cases?What is the use of the OTP function then?I lost R2984,85 on my credit card.