MTN La Lucia's Pathetic Service and incorrect Billing

This is my second experience with MTN where i have received such pathetic service with regards to my account being incorrectly charged. In December i had upgraded my MTN contract for R299 per month but i am being billed R 1600.00. I had brought this to the attention of the La Lucia MTN branch in Durban once i had received my invoice and statement for the month of January. 3 months have gone by and my account is now sitting at R 4600 as i am still being incorrectly billed, however on MTN's useless system, they can pick up that my contract is R299 but please explain to me how i am being billed twice that amount ???!! they refuse to credit my account after multiple visits and calls to the store. The manager is unhelpful and all i am told every time i call is that it has been escalated. If they escalate it anymore, my account query will be resolved by God himself. This is ridiculous as my name is at risk because these people cannot do their job.