Haveyou just switched over to PHP 8 and upgraded? If so, I would suggest first of all disabling all 3rd party items. It may be that you have a 3rd party item there that is causing issues on your hosting, and your hosting is then throwing a service unavailable at you.
As you are on 4.7.5, switching to PHP 7 is not only a bad recommendation from your host, but also not an option. The minimum requirement is PHP 8.
Your hosting company needs to tell you the reason that your hosting is showing service unavailable. That is not a message from the software. It's a message from your hosting environment