First thing I’d do is go looking for a dual set of files (an install) or something in a subdirectory off of public_html.

I’d also look at my databases to see if there’s a new database and the old might still be there. It’s also possible the new install might have added a second database ‘table set’ to the existing database.

Third, I’d go snooping around the server and see if there’s a set of backups made from shortly before this happened. Save those files off to a local PC and protect them if you find them.

Forth, I’d call my host for help.

Fifth, If all else fails then maybe you’ll either need to find a dev to fix whatever happened or find someone locally. If this is a Public Service org or charity you might find a volunteer to help.

Can you post the domain name or URL here in a reply? Sometimes I can snoop around from here and figure things out a little better.