Again, ghouse, I'm really really sorry about what happened to your account. It was wrong and we screwed up. As other comments have already noted, it was during the transition to a new security system which was designed precisely to remove the human factor from decision making.
I'm an Australian, and I'm a great fan of our "100 points of ID" system, which is designed to remove the human factor from identifying people.
https://en.wikipedia.org/wiki/100_point_check
While I wasn't aware of your account's issue at the time (and we'll be having some discussions internally about why not!), FastMail management were all aware that we needed to get the human factor out of decision making about account access, particularly since somebody tried to pull a similar swindle on our domains!
https://blog.fastmail.com/2014/04/10/when-two-factor-authent...
We spent a lot of 2016 and 2017 working on an automated account recovery system which allows recovery of locked accounts via a carefully audited set of automated steps, which includes a 24 hour lockout to allow the owner to notice an attempt on their account.
If this had existed in 2016 then we would have sent you there rather than having a human make a (poor in this case) judgement call!