Trust me, Airtel's support don't know their a$$es from their elbows.
When I called in Sept 21 about v6 roll out the character I spoke to was like "Huh?! What's that?" Don't expect answers from them because they only parrot the official line. Talk directly to a backend guy or one of the techs who install the modem etc they may know.
One more thing, check if your personal
router's IPv6 settings to /64. Which one do you use? Not sure if it has granular control over settings.