requested a paid up letter

i had a contract with mtn of which i lost,MTN elevated the matter to their legal team which is MBD,i paid up the amount that was required of me,legal fees included,then i requested a paid up letter about 4 weeks ago,they never sent it,3 weeks back i called again and requested it,i still have not recieved it and its affecting me as i cant do anything as my credit score is still showing that im owing or under collection while they were suppose to send the letter to MTN,i would not advice anyone to do business with them,too unproffessional