I'm not sure how long you've been away for, but are you logging in on here as well? https://feral-heart.com/login/
You need to use this to connect to the game, as well as keeping it open throughout the time you play to stay connected.
There is a way to change your user, yes. Just head to the home page and click 'user panel', and enter your username and password there. Once you're logged in, there's a username change setting down below. If you can't log into that as well, I'm unsure of what to do to help you. I think maybe you should PM a member of the staff team to try and solve the issue you're having.