Unjustly penalized for Cancellation of Sim Card

I have a Cell C SIM Only contract with No handpiece. My Monthly Payment is R 248.99 per month. I signed the contract in September 2021. When I signed the contract I was told that I can cancel at any time without paying a penalty as I had no handpiece. Now when I called Cell C to cancel they said that I must pay a penalty of R1150.

I have a few issues - 1 - when I called Cell C I was told that they changed their terms and conditions in Nov 2022. This can Only be applicable to contracts After Nov 2022 and NOT prior to this. As I based my decision to sign a contract based on the verbal confirmation by the Cell C staff member. 2 - On the first of this month, 1 Jan 2023, I was Incorrectly charged R267.49 instead of the premium on my contract which is R248.99. That penalty that Cell C said I must pay of R1150 has been calculated on the Incorrect premium of R267.99 instead of the correct premium of R248.99. 3 - The worst case scenario even if Cell C Don't want to Honor your Verbal Agreement which is legally binding, that I can cancel at any time without penalties, the Most you can charge me is the difference between what I would have been paying on a month to month and a contract which is R20 a month. ( R20 discount per month x 24 months which equals to R 480 ) 4 - Also the Main reason for needing to cancel is that 90% of the time I Can't connect to internet because of terrible service , So I'm paying for something I can't use.