I'm coming back after a looong hyatus (over 6 or 7 years or so), after some doing I got my account name and password sorted.
Now when I enter the game on the server I used to play (Lordaeron), none of my characters are listed. But when I go to server selection, it states I have 4 character on Lordaeron.
Below level 50 inactive characters were deleted in inactivity cleanups from non-premium accounts. Characters not in that threshold only have their names removed. Characters are prompted to be given names when you try to play them again.
If your characters were above that, and you're absolutely sure it's the right account and realm that you logged into, Warmane had no part with those characters being deleted. Since Warmane wasn't the one deleting them, that leaves one possibility: a player, a player who had access to your account legitimately or illegitimately. Said player most likely removed anything worth a dime and sent them onwards, deleting characters afterwards.