Billed even after the 24 months is up

I had a 24 months contract with Telkom which ended in October, I cancelled the contract online I even phoned their customer care requesting for a confirmation email that my contract will end, Precious Mnguni sent the message. Reason I requested for this email was because Telkom is known for extending contracts without your consent. Now I received an invoice for December, I do not understand this, I only signed for 24 months and I made sure to cancel the contract, what I want to know is who is going to pay for this bill? I did not sign for this month