Nedbank Personal Loan Payment

I have a personal loan with Nedbank and I also bank with them for many years. This is the 3rd time they have double debited the premium amount and left my account in a negative and have charged me for missed payment fees. This is ridiculous! I must then call the contact center and wait for such a long time to speak to someone to do a reversal which by the way also isnt done immediately! Pathetic service