Disconnected sim

I took a contract with telkom in 2019.was paying right until lockdown and after lockdown I went to telkom I paid what I was owing for the period of lockdown. They then activated my account after receiving payment. Two weeks later my simcard had no network n I thought mayb my contract had ended because I did not understand. I called their call centre n I was told my number had been given to someone else because I called then n said m deactivating it of which I never did. I asked them why wud I cancel a number that m receiving benefits that m paying for with?? They said they will investigate my case till today that case was never resolved n from then I had not been receiving benefits nor using the number. Today am receiving a call from debt collectors saying that I owe R200, what for exactly?