Dial 123 from your BSNL SIM and check the caller details or account info
Dial 1503 and follow the IVR prompts
Give a missed call to another phone and check the incoming number
Check the SIM card pack or activation documents
Open the phone settings and look under About Phone or SIM status
Use the BSNL Selfcare app if your number is already registered
Call BSNL customer care and verify your identity to get the number
Send an SMS or make a call to another phone and check the displayed number