You can activate DND directly through your telecom provider. Each provider has a specific method.
Jio : Go to MyJio app > Settings > Service Settings > Do Not Disturb. Select the numbers to block.
Airtel : Visit airtel.in/airtel-dnd, enter your mobile number, and enter the OTP. Then select the numbers to block.
Vodafone Idea (Vi) : Go to https://www.myvi.in/dnd, enter your details, and select the numbers to block.
BSNL : Text ‘start dnd’ to 1909 from your BSNL number and select the numbers to block.