I was in Austria until yesterday (will be there again soon) and also used HoT. For me everything worked as before with regards to mobile data. Except for loading sites in Firefox that is - but that is a Firefox issue.
Here are some questions to consider:
Are you using a custom DNS?
Have you checked whether the APN settings are correct?
Does it not show a connection at the top of the screen or does the Internet just not work in your Browser?
Have you tried force-stopping your Browser, clearing the cache and restarting it?
Have you restarted your device yet (multiple times)?
Have you tried disabling and re-enabling mobile data yet?