MTN Upgrade nightmare

Around 17/04/2019 I got a call from someone claiming to be from MTN, offering me an upgrade, which I took, being under the impression it's my service provider, MTN. Next day I called MTN to query the price difference in the deals they had online as opposed to this deal. They informed me the deal was done by a third party, and not them. I asked to cancel this deal, which they then said I have to do with Rewardsco, who did the deal. I called them, they responded that I should tell the courier company - when they call to make arrangements to deliver - that I no longer want the deal and then call them back after 3 business days, which I did. I called them again 4 days later, only to hear that there was no record of me cancelling the upgrade. I logged the issue again, but unfortunately got no ref number. I went to the MTN shop in my area, who told me the deal was still with the 3rd party, and told me to call them again, which I did. This time I got a ref no and name, and I was told to wait 3 weeks and then call MTN to upgrade with them directly. I called MTN just now, and was told there was a cancellation fee now involved, but that the contract was still with the 3rd party anyway. How difficult can a seemingly straightforward cancellation be???? In the meantime I was charged for the new premium for an upgrade I cannot cancel because of a lack of willingness (or should I say competency?) from both the 3rd party AND my service provider. After this nonsense I am definitely NOT going to do business with MTN anymore.