Mtn contracts *** service

I saw an MTN advert about a new sim card with 40G dats at the rate of R199 per month, I app**** for it by filling my contact details so that an agent can call me. Firstly I was called by a consultant from MTN taking details and I specifically told the agent that I already have mtn sim but she insisted that I can do a sim swap ,the sim card arrived it was in the sim card packaging and second when I try to make a sim swap they told me that when they do sim swap an extra R120 and must go to any MTN branch . I have never used the sim card but today they debit R458 instead of R199.00 think it's a **** service when coming to customers and would never recommend MTN contract to anyone. Kindly help me cancel the contract and they can even listen to records I was told I was gona pay R199bbut it's more.