Mtn is a ****

I have been calling Mtn for a year now asking for a paid up letter for a cellphone contract that was handed over and I paid the amount they said I should pay in full but now I can’t get a paid up letter it’s been a year requesting it and they keep giving me back and forth saying I must get it from their debt collector the collector says I must get it from mtn it’s been a whole entire year and this still reflects on my credit profile I’m beyond livid at this point