Lies and Poor Customer Care once you close account with them

I had a contract with Cell C which was closed down and paid up in January 2020 if not earlier and to my surprise the Cell C account still reflects as active on credit bureau in March 2021, they never updated the credit bureaus that the account is closed up. I called their customer service on March 17,2021 and was told that a request for a paid up letter has been logged and in 3 days time I will be called back, which didn't happen, on March 23, 2021 I called again for a follow up and the same lousy story was said. Till today 06 April 2021 the letter has not been issued neither have I even received the supposed call I was gonna get from them. All this is happening with compuscan and transunion unable to update my records till such a letter can be issued, 16 months later. Why does it even take me to get such letter for them to update the credit bureaus on a closed/paid up account...??