I’ve tried to lock up a test user in a similar way, but I’ve had no luck so far. Invites, log ins, and promotions to admin all seem to work, no matter how I mix them together.
If you have an existing account, then I think the invite link is redundant so can be safely ignored. Have you tried the basics of clearing your browser, or using a different device to log in?
Have you contacted another admin to see if they can help using their admin powers? (clearing sessions, revoking admin, etc, etc)