Poor service, wrong billing

I app**** for a black Friday data contract special which was pre approved. When I went to store (northgate) to fetch the sim card I was told that the sales assistant processed the wrong deal. I asked that mtn northgate rectified this on the system as I won't be accepting the wrong deal (till date they are still fixing this as it was not a mistake by me but by the STORE). Today (27th December) mtn debits my account for R428 and when I call mtn they tell me that this is for a R299 data contract + pro rata billing. I did not accept this contract so why the **** was my account debited? I want the monies reversed today in my bank account!!! The wrong account deactivated and the correct account activated. Idiots get this sorted out!!!