Refusal to cancel a contract

Have a 20GB data contract which I have had for many years, so much so that I am supposedly part of some sort of Platinum loyalty Programme. Anyway I used the data contract for work as there was no other service provider available. Now that I have a different and much cheaper with substantially more bandwidth available, I decided to switch. Now I need to cancel my vodacom contract. This is where the problem starts. I tried online and phoning the call centre and was told I had to go in store to doi it. I dutifully went to the vdacom4u store in Somerset West only to then be told I had to either go to the main branch or phone the call centre. I phoned again and was transferred to pillar and post and spoke to 7 or 8 different operators, answered security questions each time and all I got was all manner of excuse why they could not cancel it and continue charging for it in the meantime. Excuses ranged from my number being on an old system and they are on a new system, to the system is frozen, the system is giving me an error and more... I spent nearly an hour and a half on the line and no joy. Additionally, the 20GB contract has not been connected for the last month, the router is not even plugged in, yet I have been billed for out of bundle use of R1179!!!! During the call centre call, they had the audacity to try and sell me a new data contract. I then went to the so called big branch in Somerset Mall only to be told by the staff there that they are no longer allowed to cancel contracts because "When a customer asker for a cancellation, we cancelled it"! Apparently this is not acceptable to vodacom as it was too easy. All I want is to stop what appears to be not right and get this contract cancelled, but it is made nigh impossible