2 months since I paid my account in full but haven't received my paid up letter

I had an account with mtn which was handed over to these people. My account was 1stly doubled the amount I was owing Mt.n I managed to pay it up in full in August. Shapiro shaik promised to send me my paid up letter in 21 days but up until today I haven't received my paid up letter and the mtn account is still showing as in DEFAULT in my credit profile. I don't know if I have been ****med by Shapiro shaik oh what. I'm going to take legal actions against them now this is very painful. Using ur whole salary to pay off ur debt and you receive such a disgusting treatment. I am so angry.