Billed for a cancelled cancelled contract

I am disappointed and frustrated with the poor service that I received from Vodacom. I cancelled a contract with them a few years ago and I was billed for it.When I contacted them and logged the complaint they said that they would get back to me with feedback.Eventually they did and said that they will provide me with a refund but they cannot give me a estimated turn around time. I have been waiting 2 weeks and still no feedback was received from them.