FIRST NATIONAL BANK POOR CALCULATIONS

I took out a home loan with FNB and ever since I have been struggling with them. I'n May I received the confirmation of payment method and when they debited in June it was the total opposite. They debited R1568 from the bank which was correct and R1689 from my salary slip which was never discussed. I called them and asked for a refund of the payslip deduction and for them to cancel the salary stop order and continue with the correct amount on the bank statement. The refund was made and they promised to cancel the stop orderThis month again I experienced the same thing of incorrect amount being deducted. I called and I'm being placed on hold for more than 20minutes until my airtime runs up. If I knew that FNB has calculations problems I wouldn't have taken their loan.