Failure to cancel a contract, ********** upgrade

I took out a laptop which came with a blackberry cellphone on account at game in 2011/2 on a 24 month contract.in 2014 i finished paying off the account, december was the last month i must pay vodacom, i got a bill of 2k, i normally get billed 249 per month. i called their call center to query the debit order, i was advised i was using internet with the sim card, i choose not fight, i advised the call center consultant to cancel the contract since i wont be needing it anymore. the consultant said its too late to cancel, i must call them on the 19th of the following month. i failed to call them that following month, 3 months down the line i called them to cancel and seek a refund of the money they charged me. the call center said i cant cancel because i took out another upgrade contract at pretoria,fontana. i advised them i have never been to fontana nor pretoria for that matter, i never took out an upgrade with them. they claimed it must be a case of ***** i must send them an affidavit of what transpired, of which i did and emailed to them. i got letter after many many months of waiting for feedback saying i must pay R550 and the account will be cleared.