Debit order

Good Day am very angry with FNB I have been a problem with MTN SP ***** and I rejected the debit order on the 10th and 25th of August on my FNB BANKING app and also called FNB ***** and I was told as long as I rejected it I shouldn’t be worried and today an amount of R 2768,02 was deducted by MTN and I have also spoke to MTN on the 10th of August 2023 call REF:*** and they said it has been cancelled. My question to FNB is how was it possible for a debit order to go through without me approving the Debicheck Monday?