Opera telecom/vodacom ****

Vodacom has been unduly billing for a subscription for some opera telecom that I never signed up for since July 2015. Vodacom insists although they are receiving the funds the the vodacom bill every month that they are not responsible and that I need to unsubscribe and claim back for something I did not subscribe to in the first place. This is ridiculous and after being with vodacom for many years without any issues this is very disappointing. Can anyone assist with the legal process to follow in these instances?