Mtn must account

Mtn handed my account over to a company called Nudebt management, I paid the company the full settlement amount and I was told I will receive a paid up letter but I never received anything until today, when I go t mtn they say my account is still on legal, I called their call center spoke to an agent who was not willing to assist me she just told me their legal department does not take calls, now I want to know from mtn who handed my account to some doggy company on what to do coz I’m paid off the account they must remove my name Itc. Ref no A***