Poor service, outstanding paid up letter

My CellC outstanding account, with account number *** was handed to Blake and Associates in September 2020. The account was paid up and a paid up letter was supposed to be emailed to me, of which it never happened. I contacted the customer service department for months and months and till today I have not received my paid up letter and the account is still incorrectly "active" on my credit report. I called Cell C to do a follow up the beginning of May 2022, of which they opened a case, case no. ***. Everytime I call to follow up the consultants tell me the case is still open but they are unable to give any information. Today, 05 July 2022,I called Blake and Associates but they hanged up on me after informing me they are no longer dealing with CellC. When I called CellC to inform them they asked me to call Blake and Associate. The case has now been "edged", which apparently other consultants were not doing. I truly feel helpless and frustrated as I am in the process of rebuilding my credit score and this is a thorn in my process.