Mtn does not want to cancel my contract

Hi,my name is Nozipho Mthembu, i have an man similar contract with man which expired this year May,i called to cancel my contract with then of which when i called they would pick up and i i would explain that can they cancel my contract they would then just hang up,i called several times everyday with no success they always hang up on me, up until i got a message that they would charge me on month to month basis,i called again this time the person i got told me it would take up to 20 working days to see if my application has been successful,again it was not canceled,i have concluded that Mtn does not want to cancel my contract with them,and it really affecting me coz i am now paying every month for the services i no longer want, and it affecting my budget because i want to save, please assist me