Cell C having to many issues, cannot be trusted with a contract

I took out a contract with Cell C more than 2 yrs ago of which the initial premium was R129 p/m. Later on Cell C increased the premium, what is the point is the point of signing a contract when the supplier can alter the premiums?? Nonetheless;

Since Dec 2020 I received a number of calls from Cell C wanting to upgrade or extend the contract. I was very clear that I did not want the contract to continue, eventually I also phoned them to ensure this. still they came with weak excuses of how their system needs a month's notice just so that they can get more money?

How am I responsible for their system, was I not clear enough over the phone already in Dec, why do they continue to debit my account 2-3 months after the contract came to an end?

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