Unauthorised extention of my contract

I HAD A CONTRACT FOR 2 YEARS FROM 2015 OCTOBER TO 2017 OCTOBER YET IM BEING TOLD THAT I MUST PAY UNTIL 2019 OCTOBER AS IT WAS UPGRADED WITHOUT MY CONSENT. WHICH MEANS THE ****EN RETENTION DEPARTMENT UPGRADED THE CONTRACT TO AIRTIME ONLY WHEN I WANTED TO CANCEL THE CONTRACT AND KEEP MY NUMBER AS PREPAID... I have been going to the Vodacom shop Westgate requesting for them to assist in cancelling the contract and YET be told that I owe the contract they can't cancel after payment you tell me that it's a 2year airtime contract... I'm sick and tired with you VODACOM...........

MAKE SURE YOU CANCEL MY CONTRACT BEFORE END OF JANUARY 2018.