Airtel
Unsubscription of Game Club service

I have been getting a sms which reads:

You have been renewed for WeeklySub subscrition service from Airtel. You have been charged Rs.20. Play Games at Re. 1 http://203.115.112.5/GCLite

And I have no idea when I did subscribe to such service. And when I try to stop the service through airtel's *121*5# (Stop a service), I see that I have no services I subscribed to. How do I fix this?

Thanks in Advance..