Open the Phone app
Dial `*567#` or `*123#` to check BSNL services
Send `STOP` to BSNL customer care SMS service if available
Send `CAN FLASH` to `53733`
Send `STOP` to `1909` to block promotional messages
Use the BSNL self-care app to disable flash messages
Contact BSNL customer care at `1503`
Ask the customer care executive to deactivate flash messages
Restart the phone after the service is disabled