Contract cancelled, cancellation fee paid, but still receive invoice!

i have called Vodacom on the 18th of October and requested that they cancel my contract . i was advised that the last debit will be in November .i just got a bill for December and i called and i was advised that my contract is still not canceled and ill still be debited in December . im really TIRED of Vodacom at this point . i regret moving from Telkom to Vodacom. all i want is for VODACOM to stop the contract!!!!!!