Pay up letter

Hello, can one of you please help me get my pay up letter because its been 3 months now since I paid the full amount but still your employees keep on making me round around the circle. And come to think of the pain that I am paid for a sim card I never used because the consultant gave me false information then I canceled the contract which I ended up paying the money and now I'm struggling with a pay up letter I was told that I will get 21 days after paying the full amount.