What did you do to “upgrade hosting services”? Are you still with the same provider or did you change? Whatever the case you need to contact the original host to see what they can do.
If it’s a new service on the same host then you’ll need to contact them to find out why you would have lost the site, but if you changed host completely you might still have an account with the first host that you can use to recover the site.
Always backup!
If your old host is still running you might setup wp-config.php with the old database credentials (do yourself a favor and keep a copy of the current wp-config before you edit it. You’ll need it later.). If this works (I do it all the time on my hosts) your site will comeback up with all your content intact.
You might get a few warnings about missing plugins and such. Open a second tab from the dashboard and fix those warnings there referring back and forth to the first tab as you go. Don’t refresh the first tab until you’re done.
Once you’ve done everything to fix those warnings, install a good backup plugin like upDraftPlus and do a full backup. Store the backup files on your PC just in case then restore the copy of wp-config and when the site comes backup it will be ‘devoid of the old database content’.
Restore the database and you’ll be back in business.
Caveat: This is quite tricky but if it works then ‘it works’. If it don’t work then you might need to ask your old host for help.
Worst comes to worse you might find your old content over at archive.org. Lots of cut and paste but I’ve done that before for some clients who broke things big time!
This is why we preach ‘backups’.
