Incorrect fnb debit order

So fnb had a issue with their credit card interest and minimum payment calculationss, their own systems not customers fault. So as usual on pay day 25th I transfer more than minimum amount in my credit card. Fnb have forced me to sign debit order mandate for credit catd which I always steer clear of as it is a system to the loss of the customer. Debit order was never taken in the past but this month it was suddenly taken even though I transfered more than enough. And the money that was taken incorrectly is not available immeadiately. So what would you call it if a institution take money incorrectly from you for a day or 2. And you pay this instititution monthly for a private account. The service you get is oh it is just the system, this month has 28 days and if you want it reversed it will take R40. Should I feel my finances are safe with this institutions who can get things like this or any calculations right?