Changing of Banking details:Bad Bad Bad service

I was at the store for another contract phone with the and after doing so I wanted to change banking details, the guy at the Centurion branch named Mabandla was really helpful but unfortunately he couldn't change it from his side which he however gave me the head office contact to change with them n he attached everything to them, my nightmare is that when I spoke to the agent in the head office she told me it's impossible I have to go back to the store, she said so with confidence and arrogance and when I told her to call me her superior she told me it's not gona help because they will tell me the same thing which is going back to the store, I got so crossed and I shouted at her asking for her superior to assist me because I don't have all the time to be doing ups and downs to their store, however the line manager promised to send me an email with forms to fill in and sing and I have to even received yet, I'm so disappointed of the level of service with MTN If it was possible I would change my contact with them.