Unauthorised subscriptions charged

Vodacom has allowed a third-party, Opera Telcom, unknown yo me to debit me for subscription services I have no knowledge of. They refuse to reverse the charges. For the last 4 years I have never paid more than R100 for my 3G account and recently it has shot up. My invoice for December is R1101. How does that happen? I asked them to reverse this amount of R997.16 and was told that there was nothing Vodacom can do. I want my money back. This is an unauthorised amount that you, Vodacom, allowed to be debited!! You must sort it out.