Bul**** into contract by Buy Mondo with misleading me into chaning my current price plan on data contract

I was phoned by a lady, claiming she is from Vodacom, and that she wants to change one of my current data contracts to a cheaper plan with more data per month. I told her that I was interested in changing the plan as my dad is using this specific contract. However, she was very persistent and didn't want to take no for an answer. She said that she was going to send me just the sim card as I already have a wifi router for this contract. When receiving the sim card yesterday, I noticed that this sim had a new number. When phoning Vodacom this morning, they stated that this was a new data contract that I signed up for, and that Mondo signed me up for this contract. I DID NOT AGREE TO A NEW CONTRACT!!!!!!! I agreed to changing my current contract to a cheaper price plan! I feel like I have been bul**** into something that I DID NOT AGREE TO!!!!! I have logged a cancellation with this company, as Vodacom said that I have 14 days to cancel this contract. You state that your phone calls are recorded, please go listen to this call. And you can send the courier to come collect your sim card!!!! This is a ******** offense, phoning people and bullying them into contracts that they did not agree to!