You should have noticed when you got stamped back in that you were in fact stamped in as 30 days visa exempt because you had no reentry permit, always check when you enter. Go home. Easiest solution.
I'm confused, you need to do a boarder bounce, the alternative on any multi entry is to extend the admitted until stamp, you can do that normally on any of the entries of a multi entry, there is no need to concern yourself with what the aussie embassy is saying. I need to do a boarder bounce myself in due course, and will be obtaining an extension on it instead of risking the leaving and coming back.