Credit score damage without account usage.

I cancelled my Rain services in 2021, they have just handed me over to debt collectors in 2023 telling me that I owe them R2500. I have been calling them for three weeks trying to understand how this has come about , every time I call I am promised a call back that I never receive, I have spoken to their manager Ismael and he literally told me that they cannot do anything about my account being handed over until they confirm with their useless billing team that takes months to just view invoices. My credit score is being ruined for an account I cancelled two months ago.