Hang tight, I'm sure someone will be along that can assist you. But let me ask, did you create a database, create a user and add the user to the database?
user = the name you want to give access to
password = the password for the user
site = your-domain.ext
cpnlusername = your cpanel user name
cpnlpassword = your password to access cpanel
Hope that helps
If they just restored the database and not the other files for the forum it is quite likely that cPanel believes your forum is at the current version offered.
I would check the phpBB.com site and download the current updates and apply the patches manually.
Welcome to the forums buggurl
You could open a ticket with the help desk and they can possibly restore your database. Of course depending on when the backup was made you will probably lose some posts.
Before making any changes like upgrades you should make a backup.