Cancelled insurance but still paying for it

I took a cell phone contract with insurance in 2017, then in 2018 I cancelled off the insurance but ever since then I am still being billed for that insurance. I have been to vodacom shops, made unnumbered calls to vodacom still no help. They tell me that they can see on their records that it was cancelled but they don't know why im still being billed for it. I asked for reference number when I called they told me just mention my name