Vodacom claims payment for a contract that expired.

I had a 2 year contract with vodacom, 2 months before i called to notify them that I was not going to renew contract and the number was cancelled on the last day of the contract by vodacom ; Now I am getting sms claiming that I owe them money and they will not close the account until the money is paid. They were deducting money from my account via debit order and I don't understand how i could owe them money. This is day light ******* and I will never ever get a vodacom contract cell phone again. ACC:9l **********