Update as of 1st Sept 2019 - ACT customer servie informed me on a call to my inquiry that v6 is no longer offered; they only activate WAN side v6 when the dynamic IP pool is congested and normally v6 is not offered. Even funnier is business customers with static IP's are never presented with v6 and are stuck with v4 alone. Pity as v6 will soon gain wider adoption in India after Jio comes up with its home broadband.
Update as of 30th Sept 2019 - Not sure what happened, I am fully getting WAN side V6 now; it can mean two things - either the load is constantly high and thus V6 is available or they just started activating V6 full time. Either way, IPv6 is active and usable with ACT.
ACT after testing it out in Bangalore, has now enabled IPv6 in Chennai; making ACT as the only ISP after Jio to provide services in IPv6.
Right now they're using 64 prefix.
Sites to see if you are IPv6 enabled:
http://v6.testmyipv6.com / http://ds.testmyipv6.com
Recommended IPv6 DNS:
2620:fe::fe / 2620:00FE:0000:0000:0000:0000:0000:00FE
2606:4700:4700::1001 / 2606:4700:4700:0000:0000:0000:0000:1001
2001:4860:4860::8888 / 2001:4860:4860:0000:0000:0000:0000:8888
2620:0:ccc::2 / 2620:0000:0CCC:0000:0000:0000:0000:0002
2606:4700:4700::1111 / 2606:4700:4700:0000:0000:0000:0000:1111
2620:0:ccd::2 / 2620:0000:0CCD:0000:0000:0000:0000:0002
2001:4860:4860::8844 / 2001:4860:4860:0000:0000:0000:0000:8844