CONTRACT EXTENDED WITHOUT MY REQUEST

MY CONTRACT FOR A SAMSUNG TABLET WAS TAKEN OUT FOR 2 YEARS ON 14/1/2014. I HAVE BEEN PHONING VODACOM FOR THE PAST FEW DAYS TO ENQUIRE AS TO HOW TO END THE CONTRACT AND TO GO ONTO PREPAID AS THE PERIOD HAS NOW COME TO AN END. THEY INFORM ME THAT THIS CONTRACT WAS EXTENDED ON 5 OCTOBER 2015 AT A COMPANY LIKE MINDS IN DURBAN.I LIVE IN CAPE TOWN AND HAVE NOT BEEN TO DURBAN IN YEARS. THEY CANNOT SUPPLY ANY PROOF OF THIS. NORMALLY FOR ANY CHANGES OR UPGRADES THEY REQUIRE A LETTER ON A COMPANY LETTERHEAD AS WELL AS MY ID. THE PROBLEM NOW IS THAT THEY WILL INCORRECTLY DEBIT MY ACCOUNT AT THE END OF JANUARY 2016 AND POSSIBLY FOR THE NEXT 2 YEARS. I HAVE BEEN PHONING VODACOM FOR THE PAST NUMBER OF DAYS WITH NO SATISFACTION AND THE LAST CALL TODAY WAS FOR OVER 50 MINUTES