Contract upgrade

I have a contract with mtn , my contract is due for an upgrade. I received phone calls from consultants so many I told them all that I don't want an upgrade I will be cancelling my contract on the 26 of December after my last payment . on the 25th I received another call from MN again I told the lady that I have spoken to the consultants and I won't be renewing my contract she said okay its fine. On the 26th at round about 15:49 I received an SMS stating that my upgrade was successful and I have received 100 free minutes , then I checked my phone there was 60 free minutes and 125 smses and data I don't know for how much as I already had more or less 200 data in my phone. I phoned mtn I was told I will have to go to a police station and make an affidavit . on the 27th I I tried to make calls I couldn't my Sim was suspended, so I went to the nearest mtn store . the consultants at woodlands boulevard were so helpful they even checked on the system and they did confirm that the upgrade was done. And there was a Samsung s6 that was taken on my name . I really don't get it , how can an upgrade be processed without my consent, I will never ever take a contract with mtn