Wrong and ********l debit deduction

On/about 21 August 2017 we became aware that Cell C debit our account in the amount of R 636.99 while we have no agreement or service with Cell C. We contacted them and request to stop debit our account, which they promise to do. The reference they gave us is: ***. They refuse to give us any details of the account and say it is privilege information and as we are not their client they are not at liberty to reveal any information. To date they have not stopped the debit order and/or refund us for monies wrongfully deducted from our account as promised. On the contrary they again deducted the same amount on 31 August 2017. Notwithstanding numerous calls to Cell C it appear that they are unwilling and/or reluctant to resolve this matter. My question; How can Cell C debit any account without verify the account holder?