How to disable flash messages from telecom carrier?
These Class 0 messages are also called flash messages, that can be disabled by :

Calling Airtel service and requesting (personal experience)

On your device (SOURCE that lists methods for other  Indian carriers also)




Open SIM toolkit application and tap on Airtel Now! service. Now click on Start / Stop and select Stop to deactivate flash SMS completely.

In addition, you can also message STOP ANOW to 58234 to request the service deactivation.