My account/character has been hacked

I logged in my account today (since 1 week ago) and 1 character has been hacked recently. It has 0 gold, few items, 0 emblems, etc etc.

What should i do to recover all again? (like a back up data to return my character 8 days ago, maybe other solution)

Is it possible to get something stolen back? (at least to start again to get all)

What to do for preventing this again? (i already did the authentication security thing but i would like to be sure this will not happen again)

There is nothing that you can do and GMs won't give you anything back (except perhaps things that you purchased using coins).

Activating two-factor authentication is good enough. If it's email-based authentication (a code that you receive in your email) make sure the email is also well secured.