mtn cellphone contract dispute

Morning, I have 3 cellphone contracts with mtn and of which 1 came to an end past November and the other coming to an end this month and the third 1 will end August, I been trying to call mtn to cancel for the past 3 months with no success, I even went to their 2 stores of which the one is in Glen Marais and the other in festival mall but was told they can't help me cancel as they don't have cancellation system,was told to call mtn or either go to greenstone as they said is the main branch, I been trying to call them several times for cancellation but they don't answer my call, I will stay for more than 20 and sometimes 30 minutes on the line without an answer, their main branch from greenstone called me on the 3rd of February asking me if I wanted an upgrade and I told them I want to cancel those 2 contracts , and the lady that called told me she can't help me to cancel but can only help with the upgrade, all in all those 3 contracts where R357 and when the first one came to an end in November my installment was reduced to 283 , 2 of dose contracts costed R130 for 2years and the other was R99 for 2 years also, so the lady from greenstone mtn branch told me she can only help me downgrade to pay around R87 for 3GB for 2 years and I ended up agreeing to something I don't want just to reduce my installment, so no longer want anything to do with mtn, I won't even recommend anyone to take contract with mtn , I fill like they holding me hostage, my number is ***, will be Happy if I be helped