Cell phone contract went wrong

I had a contract with Telkom that was ending in March 2024. I went to the store to cancel in April they told me I am owing R338. I paid R200 on the 1st of April and asked them via email to cancel and they responded by saying they are sad to see me leaving and I asked me for reasons. I don't know if was a system I was talking to but was kind of pop-up message. I regave them reasons and sent the message of cancellation. But they billed me in May and I didn't pay ,they then block cked my number in June and registered my name with credit bureau.

They are still harassing me that I should pay via calls, emails regardless of I have send email to cancellation department or not and I am not even using those datas and airtime but they bill me until to date for data and airtime I didn't sign for and not even using because they blocked my number. Please help me how do I solve this matter? My credit record is dented.