The MOO reaps characters after a certain amount of time but the website doesn't get notified about that currently. It's on our list of things to fix. The solution here is to connect manually, either with your favorite telnet / mud client, or our webclient https://play.sindome.org/
Despite the website saying you have a character still (and you knowing differently), the MOO know's what's up and will let you create a character!
So connect as a guest (connect guest on a mud client) or use the 'connect as a guest' option on the webclient.
Once connected you can use the @register command to register normally. Go through the steps of confirming, etc. and then go through character generation. When you are done with character generation you can use @claim or the website claim form to claim your character into your website account!
Hope this helps you, and others in the future.