Call up 1909 and follow the IVRS instructions. It is a toll-free number and hence you won't be charged for that.
Activating Do Not Call using SMS.
The number for activating Do Not Call registry is same as the IVRS number, ie., 1909.
Send SMS to 1909 with one of the below options.
The above message deactivates all the promotional calls and SMS, however, you would continue to receive important transactional information from Banks, your mobile operator and communication issued by Government of India.
Kindly note, STOP 0 and START 0 have the same effect.