Pathetic Service when you want to cancel a contract line!!!!!

I have been trying to contact MTN's Retention's department since 17 August. I have had a contract with them for over 3 years and payments and service have occurred without fault. On my contract, I have 3 separate lines. 2 of these lines are due for upgrade and since August, I have been trying to get them to change the one number to prepaid.

The Upgrades Team called me weekly without fail telling me the lines are due and each time I ask for the Retentions Dept, I am transferred and the call drops or when I call them myself, I hold for over 20 minutes at a time. I know a churning customer may be a little hard for MEGA telco you are, but I'm certain my 1 line won't bankrupt the business SO TAKE IT TO PREPAID!!!!!!

I have asked for help via email. I have sent messages via Twitter... and nothing!!!!! Pathetic service!