Loan dispute

I am extremely unhappy. I have a loan with FNB, the loan agreement states that my monthly installment will be deducted on my salary day. Every month they deduct a week before my salary day and the charge me interest every month. The toll free number gets no answers. Two call me back requests, personal banker messages and still no feedback. The loan department I can't get through when phoning from a landline. Paying interest of R100 every time when that's not what the agreement was???? And still no feedback???