Really sorry this happened to you. I don't have any advice about how to contact support, hopefully someone else does.

One piece of advice I've seen for people in your position however is to try to contact your friends, FC members etc. through Discord or some other source. Have them report your character as stolen and forward any info to support. That way your character can get a (temporary) ban to limit the damage. When you get control of your account again Sqeenix can remove the ban and possibly to do a roll back to before the breach.