No assistance received from Nimble group

I had an MTN account back in 2021/2022, which was settled and closed the same year. Around April this year (2025), without any communication, I saw on my credit report that the account was still in arrears and had communicated with the Nimble group several times and even sent the paid-up letter from MTN, but still remained active until now. After so much communication with them, this still affects my credit score. Yesterday, I communicated with Immaculate through CHAT BOT regarding the matter, and was advised to request the paid-up letter within 48 hrs. Today I am trying to visit the CHAT bot, but it doesn't go through. I do not know whether I am blocked or what.

Can I please be assisted with the paid-up letter and removal of the account on my credit report? This has been ongoing for a long time without changes.