I’m very sorry to hear of the trouble this is causing for you. I would advise not waiting for our support team to answer a ticket about this, as they will not have any direct insight to share and they actually have less access to your server than you do.
I would check /var/lib/mysql and see if the databases you are expecting to be present are actually present there. If they are not, you need to restore your backups. If they are there, then perhaps they are not owned by the correct user. You could try:
chown -R mysql. /var/lib/mysql
systemctl restart mysql
Those commands may vary slightly based on your situation, but cover a vast majority of default setups.
If they are listed in /var/lib/mysql and the above commands did not change anything, what user are you connecting to MySQL command-line as? Make sure it is the root user for good measure, so you can rule out specific issues with user permissions.
If all else fails again, restoring backups is probably not a bad idea. Spending hours hunting the “why” may not be the most productive way to get back online, regardless of it’s importance.