Cell C cancelation

After my contract expired at Cell C, I canceled the contract. Cell C kept deducting money on my account. I reversed the debit order. Cell C handed me over. But they cant help me on the phone or via email to provide the recordings of the cancelation. Even if I provide the date and time of the call. No one can even tell me why they still deducted money on my account. No help. Only handed me over for collection. I cant even upgrade my other numbers at Cell C because of this. Why cant they tell me for what was the deduction for or help me with the recordings?