Cell C nightmare part 2

I cancelled my Cell C contract in November 2020, and they kept debiting my bank account so i stopped the debit order till the matter was resolve. Thank goodness they finally paid attention and fixed it. However now i received a whole other surprise, i have been handed over for +-R500 that i do not owe. And the best thing is that i am being threatened. My Statement that i received in June 2021 they owe me money. I have asked for a paid up letter four times now and all i get is an escalated case. I am so fed up with Cell c and their inability to help a person. I was told that this is affecting my credit score and i want this sorted out immediately.