Blacklisted for non payment for R0 balance account

I have been blacklisted and showing no payment on account from 2018. I was under the impression this account had been closed until i checked my credit score and it showed Telkom as R0 balance, but that i have missed payments from 2018, bringing my credit score down. When i called, they could not find any communication to me where they advised that my account was in arrears or that they would be blacklisting me, which i know is *******. No one may be blacklisted without being informed of an outstanding balance. My account shows R0, yet they say i am in arrears!