Trying to cancel my contract for the past 3 months

I have been to two branches in Centurion to cancel my two MTN contracts, first they told me to contact the call centre, so I did (after waiting for an hour on the phone), the agent then told me that the contracts were cancelled and that the lines will be converted to prepaid in 72 hours, I have waited for 5 days but still no cancellation. I then went into the centurion branch to find out and they told me that the contracts were not cancelled. I they then told me that they will cancel it and gave me the reference numbers *** and *** for the two contracts, but to this date the contracts have not been cancelled and I am stilled being billed every month, What do I have to do!!! you are not cancelling my contract and charging me upgrade fees for both numbers on my statement as well as still charging for handset fees but the contract expired 2 months ago!!! Please all I want if for my contract to be cancelled and converted to prepaid why is it so difficult !!