Samsung - Airtel Prepaid — Getting all junk messages which is disabling mobile operation for sometime

For about a month I am receiving messages from porn sites, pharmacy sites, etc. The message is received with the following details:

Call cost: Rs. 0/-

This will lead to a chain of messages minimum 2 in count.

Whenver I receive such message, the functionality of the mobile is diabled for about 15 minutes after which the mobile gets activated automatically again.

Sometimes I may receive calls from such numbers. Incoming call keeps buzzing and the mobile functionality gets de-activated

Kindly look into the proble mimmediately.