Con Artists - How does MTN allow this?

I was called by an agent of Summer Mobile, representing herself as an MTN agent, wanting to 'help' me with an upgrade. She sold me an improved package (at a higher cost but with more features) but neglected to tell me that it was over a 3 year period, instead of the standard 24 month. When I realised that I would be stuck in the contract for that length of time, I gave clear instructions NOT to go ahead with the upgrade. But.....within 24 hours I received an SMS congratulating me of my new upgrade. I immediately called SUMMER MOBILE and asked them to once again cancel the upgrade. Vincent the call agent said it would take 7 days to process. 24 hours to switch on...but 7 days to cancel! 7 days later....I was credited with my upgraded minutes & data - no cancellation! I have just spoken to SUMMER MOBILE call centre again....now they say another 24 hours. And they blame my service provider MTN for the problem. Be very careful when you receive a call from a so called 'MTN agent'. Maybe MTN you should be more selective on how you are represented by 3rd parties. I'm going to port across to Vodacom.