Unwanted Billing

I have been randomly subscribed to a paid for service that I do not want, and did not request. That cannot be legal.

"Y'ello. Thank you for subscribing to MTN Gamer+ at R3.03/day or a lesser amount. 1st day is Free. Visit now http://gamerplus.mtn.co.za/. To cancel dial *155#. Call 135 for help. Ts&Cs www.mtn.co.za."