Mtn is over charging my account and breaching their contract!

I took a black Friday upgrade contract with mtn for R299.00 per month but mtn is charging me R1299.00 per month from 27 November 2020 until May 2021 I have made several calls to their call centre with no proper feedback. All I hear is we are fixing the issue but months later nothing is being done. When I go to the Mtn Galleria branch the sales person Sandesh tell me its head offices fault. When I call head office they say its the stores fault. Sandesh further goes on and tells me to cancel my existing contract promised by the store for a another unreasonable contract. 1299 for 36 amounts to R46 764. For capped data how ridiculous is this. Their actions have lead me too believe that Mtn are ******* praying on customers and frustrating them it is not a safe environment to be i wouldn't recommend anyone to them.