I have been trying to cancel my Data contract with Vodacom and I'm not winning

I have been trying to cancel my Data contract with Vodacom and I'm not winning. I have been billed but not used their data which they expired. I made a payment for the data that I didn't use, I was told I won't be billed but still being billed to date. I sent emails and called but not getting help at all. So disappointed in Vodacom.