MTN overcharges and poor customer service

I took out a contract on black friday 2018, the deal I took was a sim only deal, 20gb of data for R199 per month, however, from March 2019 I get charged R319 every month.

I have contacted the call centre and the store on various occasions before, the one assistant from the store in westgate advised me that they were not discounting my statement in accordance with the black friday deal and that he has informed the lady who dealt with my contract to contact me.

I was never contacted and tried the store again, the guy then advised me to go to ANY MTN store to sort it out, I now live in the east so I went to an MTN in the east, and offcourse thedy tell me they cannot help without a copy of the contract, the lady who initially assisted me also told me that she would send me a copy of the contract to my email address as systems were down on black friday, which obviously did not happen. I do however have email proof of the deal. I laid a complaint and have been following up since the beginning of last year... Around May, the lady did begin responding and assured me she will send my contract as well as correct my billing. But when I followed up after yet another month of being overcharged - no response. So 2 years of being overcharged by R119 per month, but they can surely get someone to call and ask you if you would like to upgrade etc. Pathetic