The site works fine for me, since you upgraded to premium it’s likely you’re experiencing DNS cache issues (where your computer still thinks you’re on free hosting).
The following article has some tips on how to deal with that:
Additionally, since you’re on premium hosting you should check their client area instead of InfinityFree’s:
I’m almost certain that happens because this is a private directory that isn’t meant to be accessed by outside visitors. The rest of the site seems to work fine.