Hello,
I am sorry to hear about these issues. In the first instance I would suggest connecting to your site via S/FTP or using File Manager through your host admin panel. Try renaming the plugins folder to plugins-old and attempt to access the /wp-admin login page. Do the same with the themes folder. If this does not work you might need to contact your host for further advice.
In terms of restoring without any access whatsoever – you could create a new WordPress instance and install UpdraftPlus. Connect it to the same Google Drive account and click UpdraftPlus >> Backup / Restore >> Rescan remote storage to add the backups to the database and restore from there.