For those who are facing this issue i got something for them. Please guys go to Nokia service centre and ask them to install May security patch in your device. Your problem will be solve within 20 minutes if they have May patch if they don't have it then it will take maximum 24 hours to update your device. Please do this if you're facing VoLTE problem after June update. Trust me guys i was also facing this since 16 June. Nokia service centre in Rajkot i went there they solved this in 24 hours. Go to your nearest Nokia service centre.