.tun file missing in HTC desire 816 G

Actually i had rooted my phone using kingsroot but due to some problem i unrooted & then made a factory reset...BUT now i am trying to root it again but phone fails to do so...
& when i install any VPN it does not get install, in case few get install then does not connect & in some VPN " .tun missing" error comes...
pls help ASAP.