Hi Charles,
I’m sorry you’ve had such a bad update experience.
If you are comfortable doing so, either via an FTP application or the file manager in your hosting control panel (if there is one/if you have that kind of environment), could you try navigating to the theme directory and create a new folder in there called something like __temp – then, move the Divi directory in there.
This should forcibly deactivate Divi and – hopefully – you can then access the admin environment. Perhaps you could switch temporarily to a different theme (such as a default theme) as a stop gap measure until we can determine the problem with Divi?
It may also be worth reaching out to their team, if you haven’t already done so, to ask if they are aware of this issue and if they have any advice on resolving it.
Does that help in the short term? Definitely keep me posted as things progress.