Unautherised Subscription Service

For the past 3 months i have received my invoice from telkom and i have noticed a charge of R217 on all 3 my last 3 invoices claiming i have subscribed to some content service for R7 a day. i have not authorized this on my mobile number and to to top it off my mobile sim card has been switched off for months i do not even use this simcard Telkom seems to not know what it is and is not able to stop or cancel the subscription service!!!how do i find these people and what do i need to do to get my money back, please help!!