incorrectly handed over for a paid up account

I had a cellphone contract with MTN, it fell into arrears and was then handed over to Nudebt. i made arrangements with Nudebt and then paid the settlement amount in January 2025. Early March when i checked my credit report i found that i had a new listing from Nimble group. when i did follow up i was told that MTN has yet handed the same account over again to Nimble. i have called Nudebt and they have been saying they have requested for a delisting from ITC and that they have also escalated to Nimble but still the account is updating further arrears on my bureau. None of them is willing to account for the mess creating. i keep on calling and sending emails and i am not getting proper assistance. i am in the finance and insurance industry and this is negatively affecting my chances of employment /promotion because arrear accounts are taken into consideration during application stage.

the service is very appalling.