First, I'd contact your state attorney general's office. See this link to usa.gov for a contact database: https://www.usa.gov/state-attorney-general || https://www.naag.org/find-my-ag/
Next, contact your representative in the House and both your Senators: https://www.house.gov/representatives && https://www.senate.gov/states/statesmap.htm
Then I'd reach out to the FTC (Federal Trade Commission) with a formal complaint: https://reportfraud.ftc.gov
Filing a complaint with the Better Business Bureau might prompt some movement, even though AFAIK they have no real power over anything, but reputation damage may be threat enough to get them to play ball: https://www.bbb.org/file-a-complaint
And for "the big one": reach out to journalists in the tech industry. Posting here at HN is a good first step, but I'd tell every tech journalist who's got ears (or eyes) what's going on and see how many of them pick it up. Hopefully enough to cause some real damage (because, sadly, they've made it clear that's what it'll take to get them to stop holding you hostage).
Finally, contacting an attorney for at least an initial consult can't hurt. See americanbar.org for a list of attorneys admitted to the bar for your state: https://www.americanbar.org/directories/bar-associations/
I don't envy you, and I'll very likely never use Notion now that I've heard about this. How can anyone trust them when they literally hold their own customers hostage, ally the while lying about why they're doing it?