Farud line added to my name and also Cell C customer care refusing to take my written email cancellation.

On the 02 May 2024 after I emailed Cell C to ask that they cancel my contract due to the fact that it had already ended. Now I was on a month to month contract which now moved from R450 which was the contract I signed up for. Now the contract has increased to R1160. Without my consent, Cell C place me on a contract which is double my previous contract without my approval. Also they are refusing to cancel my contract saying the written email which I sent on the 02 to cancel my contract is not effective and I should have called instead of submitting a written notice to cancell the contract. I have proof of the email and also received a ref number for the amil which was sent to their cutomer care email. But they still refuse to cancel the contract starting on the datye which the email was sent.