Error establishing a database connection

I’ve been using this website and updating it fine. Took a week or so break and came back to find this message. I’ve contacted the host and doesn’t seem to be an issue on their side. I did look at documentation but feeling lost. wp-config seems to be set correctly.

Error establishing a database connection
This either means that the username and password information in your wp-config.php file is incorrect or we can’t contact the database server at localhost. This could mean your host’s database server is down.

Are you sure you have the correct username and password?
Are you sure you have typed the correct hostname?
Are you sure the database server is running?

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