DMC TERRIBLE SERVICE!!!

I have been waiting for months for DMC to close my account on their end, as I have been handed over by Cellc, I have paid up this account in September 2023, Cellc has closed the accounts but DMC still has this account open and this is causing my credit score to drop month after month. I have request for a manager or team leader to call me back but no contact has been made, Terrible customer service from DMC!!!!! I need this to be resolved as I don't owe DMC anything!!!