A company not to be trusted

I upgraded my MTN contract on 1/3 to a R469.00 top-up contract. When my data is depleted I purchase data. My debit order was fine until May, when I suddenly started being charged for usage.They overcharged me by R858.30. I tried to contact their call centre, but they are on strike and the call centre is not operational. I lodged a complaint online. I went to my local MTN store in Kenilworth Centre where I spoke to Hieshaam. He lodged a fault on their system and said that I will not be refunded, but instead a credit will be placed on my account. I told him that is no good for me, as I live on a budget and cannot afford to pay almost 3 times the amount that I am supposed to pay. He said he will request a refund. On 12/06 I received an sms from MTN stating that my credit request has been sent for approval. Yesterday I received my new MTN statement reflecting an amount of R522.48 due, which is a R53.48 overcharge again. I again tried to call the call centre and I also tried to call Hieshaam, with no answer. I took time of work and drove to the Kenilworth store. They could not help me either. Jamielah was on duty and she refused to do anything, just said lodged the fault, I need to wait