Continuous Debit After Contract Term Ended

I had a vodacom contract that came with a laptop and data only sim card which was paid in full and contract was coming to an end in October. I called in September to ensure the co tract is not renewed. I stopped using the sim card upon cancellation of the contract. They continued to debit my account of the contract amount regardless of my request to not renew. I have repeatedly contacted then thereafter and they have still continue to debit my account and not cancel the contract.