Im stuck for almost a week here.
I tried to enumerate dns by bruteforce and found 2 domains.
I tried to zone transfer to ns, but it failed.
I tried to zone transfer to main domain, but it failed too.
fierce failed too
I tried subbrute too, but it just produces error and taking forever.
What to do now? 
EDIT: After a few seconds of posting this. I just found it out. lllllllllllllllooooooooooooolllllllllllllllllllllllllllll