Adverse credit rating because of incorrect reporting!

I previously had a credit card which went into arrears but was subsequently settled in 2017. Last week while checking my credit rating, I was shocked to see that the same account- which was settled ages ago- appears as in arrears, decreasing my credit score as a result! All my accounts are up to date and this has set me back greatly! I phoned (last week on Tuesday, 12h39- Legal Dep) and spoke to a Londiwe. I was promised an SMS and settlement letter. Nothing to date. I just phoned again today and spoke to a Cergilo (Legal) at 14h33 and was first told I would get the letter within 3 working days which is absolutely ridiculous. Both Londiwe and confirmed that the account is settled so why must I wait- from last week- for a simple settlement letter?! I refused to take this and was told it would be sent today. Honestly, I'm not holding my breath. The account is paid up, why am I dealing with this and the red tape around getting a simple settlement letter?