First of all go in the settings of your phone then go in mobile networks then you will see volte calls bsnl. Switch on the volte calls bsnl then just below the volte calls bsnl you will see network mode bsnl in that select LTE/3G/2G ( auto connect). Then come back and download the bsnl selfcare app from play store and login the app using your bsnl mobile no and after loging in you will see support option in the lower portion of the app. Open it and you will find new complaint in that you will have to register your complain so in the first option of account type select your phone no in which your volte is not reflecting then in the second option of District select your district then in third option i.e. city/village select your city or village then in the fourth option Complaint type you have to select the option of service then in the fifth option i.e. select the issue select first option which is no incoming calls then in the last option i.e. Remarks/Describe type please activate my Volte as soon as possible and then press on proceed. Your complaint will be registered and you will receive message regarding the registration of your complaint and within 24 hours or more your volte option will be activated by the Bsnl operator so for that you will have to check your selfcare app in the option track complaint. You will receive their the message that your issue has been resolved from the operator.
I too have activated my Volte in bsnl 4g sim by the same process.
