Mondo upgraded my contract without my consent!!!!!

My Vodacom contract expired to which I kept it on a month-to-month as it suited by budget and my handset is still in good working order. However, earlier this year I got a call from Vodacom Rewards aka Mondo so say that they can reduce my monthly payment while increasing my value since my handset was already paid for. I specifically asked them if this will still be on a month-to-month contract to which they agreed. I phoned Vodacom earlier this week to cancel that contract to go over to prepaid as we got wifi at home and it is a waste at this stage to pay for a monthly contract just for airtime. To my shock I was informed that Mondo upgraded my contract for two years without my permission. Vodacom cannot cancel this on their side, and said that I need to contact Mondo directly. I have been waiting for feedback from them since Tuesday! I want answers and my contract cancelled!!!!!