Dial 123 from your BSNL mobile number
Dial 1503 for BSNL customer care
Dial *222# on your BSNL SIM
Check your SIM card pack or welcome message
Use the BSNL Selfcare app
Check the number in your phone settings under SIM details
Call or send a message to another phone and see the caller ID or received number
Visit a nearby BSNL customer care center with your SIM details