Cancelled 3G line in April 2017 - Account debited until second cancellation in October 2017

Phoned in to the Vodacom call centre on the 04/04/2017 to cancel my 3G line which was no longer being used. The call centre agent advised me that i need to confirm my instruction in writing, as the contract needs to be cancelled in that manner. I duly did so, and emailed ********** . No response was received, despite emailing twice. I have noticed this morning on my bank statements that this debit order has been running since April, and i demand to be refunded the amounts ********ly debited on my account.