Mtn 3rd party telemarketer that doesn't know what she's doing

I was called by a telemarketer thru mondo for a MTN cellphone contract I clearly told her I was interested in the Samsung A21....come to find that she put me up for the A12 and for 36 months where the advert says 12 months. The headset is yet to be delivered but I won't be taking it. In contacting MTN they gave me a reference number via email and has yet to call me back. How can these telemarketers just decide you want a phone and should just pay for it. Cancelling something you don't want thru 3rd party is a hassle!!and then she (the telemarkter)proceeds to go about it asif shes doing me a favour and saving me money.********** PEOPLE I TELL YOU!