Facing issues while flashing stock rom of Lollipop/Marshmallow

Hi..
I am using Moto g 2015.
I unlocked my bootloader,,Flashed cm12.1 and using since 5 months...
Now i got Jio 4g sim and Using it..(India)
Data services is working perfectly..
But i am not getting VolTe sign and even option to enable it anywhere!!
I heard somewhere that we need to flash stock rom to use VoLte feature..
And then I tried to flash stock rom ..
And then i am getting remote failure..
I am starting with
fastboot flash partition gpt.bin
And there is remote failure issue with flashing Marshmallow and also while flashing lollipop 5.1.1
I am using XT1550 INDIAN 2GB VERSION..
Issue with Jio4g VOLTE :- I am unable to listen any sound from another while calling over LTE..
I have putted 4g sim on sim slot 1..
Pleaae help me to flash ..
Thanks