Capitec Unauthorized debits from Accounts!

Capitec Bank decided to debit from my Capitec savings account instead of debiting from my FNB Cheque account that I authorized them to debit from. The money they decided to debit was suppose to pay for something else. It is such an irregularity to take money from an account that I did not authorize them to take from. This bank does Mafia/street things that are not allowed, since well they are doing this...I have decided not to pay their loan, TIT FOR TAT. The call center agent was so ride and shouting at me, bad customer service!!!!