How to deactivate Monthly Masti service, BSNL ?

I used to get a SMS every month, from BT -ONMOBL, saying :

" Thank You for continuing Monthly Masti service. You have been charged Rs5. For other exciting subscription packs details, SMS HELP SUB to 56505. "

But I've not subscribed to any of such services. Its very hectic and fraud. BSNL is grabbing the money from consumers without any consent of the consumer. Searched this in internet, and to my surprise I found that, there are many people like me, who are facing the similar problem. Somewhere in the internet, found a way to unsubscribe it.

To Unsubscribe :  Send CAN MASTI  to  56505. Then they will ask for your confirmation to unsubscribe, by sending the following SMS to you.

" Dear subscriber, To confirm your cancellation please send  
 CAN  MASTI  YES  to  56505 "

That's great. To activate the pack, they won't ask for your confirmation, but they strictly need it to deactivate it. And for each of  these SMS s, they will charge 2 Rs. But any way, 2+2 Rs. is better to loose than 5 Rs./month. Is n't it ?

Praise the BSNL..!!