Error establishing a database connection

Hi All.I’ll try and explain the best I can.
I’m quite distraught as my website has gone so I really hope you can help.
I’m getting the following error – Error establishing a database connection.
I’m trying to get help from my hosting company but without telling anyone it’s changed hands and the new support is terrible to non existent.
My website has a forum and ‘had’ a wordpress home page.
It looks like the database SQL file for wordpress has gone has just gone.
The forum one is still there but not the other one.
I’ve asked time and time again if they could restore a a backup but they haven’t done it.They keep promising to call me back but they don’t.
I can’t see a backup for the missing one on the hosting panel.
The last email I got from them tells me that ‘We’ve restored the db ‘missing one’ to a new Database. This new one contains no data.

Even though my website is 23 years old I have very little SQL experience

I have all the files but I’m really stuck about what to do.

Thanks

The page I need help with: [log in to see the link]