Cancelled Contract - yet being billed

I'm so ANGREE with Vodacom. I've cancelled one of my contracts that expired - TWICE, received confirmation emails, spoke with 4 different call center advisors, which confirmed or cancelled the contract again. This was attempted 4 times, yet I once again received a invoice with the cancelled contract amount billed. Several advisors advised that they processed the refund that was deducted from my account incorrectly. I have several reference numbers, etc. Yet no success! Can anyone please help.