There's only a handful of possible causes here:
- you deleted your characters
- you accidentally made them on a different server, thinking it was Green (have you checked Blue and Red?)
- you made the characters with a different account (and, maybe, also on the wrong server?)
- you made the characters on the correct server, with the correct account, and didn't delete them ... but some freak accident did
Maybe others can chime in with more, but that's all I've got ... and I really don't think it's the freak accident one, because we've heard a few of these stories over the years (hell, I was responsible for one), and I have never, in almost a decade of playing here, heard of an issue with characters just randomly getting deleted on the server.
I'm not saying it's impossible, just very, very unlikely. And that leads us to the earlier bullet points: I'd check every login there's any chance you might have used, and check every P99 server (heck maybe non-P99 ones) for those characters.