MTN - Unacceptable service

I have for the past 3 or 4 months being dealing with MTN and their customer service center and I am seriously not impressed. Due to affordability I have been trying to downgrade my account. Every time I call in I am told that there is amount outstanding and am told to pay the amount and send proof of payment and then it will be up to date and I will then be able to downgrade. Well after numerous phone calls and payments this has still not happened!!!! I have spoken to supervisors and sent the relevant forms. What more do I have to do. I keep getting cut off even though I have paid the amount everytime as per what I was told. THIS IS TOTALLY UNACCEPTABLE