Cell C upgrades your contract WITHOUT your permission!

I received a phone call from their Call Center regarding upgrading my current phone and contract. I DECLINED and said I would like to keep it month to month with NO new contract or phone. The lady stated my new payment would be approx R620 per month and I agreed. The following day - LOW AND BEHOLD - I get a call from Cell C congratulating me on my UPGRADE!!! The immediate month after the call, my account was indeed in the region of R620. But to my surprise - the following month it shot up to R1600 - my UPGRADE which I never agreed to was nicely in place, money is deducted from my account, and here I sit - NO ONE WILL EVEN BOTHER TO FIX THIS and I have sent NUMEROUS emails in replying to their congratulatory emails to STOP THIS CONTRACT!!! It's like chewing bricks and if and when you DO get to speak to a human being - they simply do NOTHING!!! I am so disappointed in them and being in the middle of a pandemic for them to abuse ELDERLY people like this, is even MORE disgusting!!! As soon as I am able to visit their store, I will go there in PERSON and SIT UNTIL I HAVE MY CONTRACT CANCELLED AND A FULL REFUND HAS BEEN ISSUED!!! And if it takes a week to do this, then so be it. Maybe THEN they will train their call center staff to actually LISTEN to a person when you say NO!!!