Your boards likely were moved into a Workspace:
And you had more than 10, so the least active boards were closed (not deleted).
Welcome to the Atlassian Community!
Trello still has a free plan, and that is probably never going away. See https://trello.com/en/pricing for the options and comparison.
For your boards disappearing, that's a totally different question. We need to know what has changed - your login maybe, or has someone claimed your Atlassian account that you were using for Trello. You say "lots", is that all your boards, or just some? Is there a pattern to which boards have gone?
Congratulations to @Laura Holton , our latest winner of Taco Tuesday! And thanks to @Kristján Geir Mathiesen for sharing the picture of Taco having fun with his new friend B...
Connect with like-minded Atlassian users at free events near you!Find an event
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no Community Events near you at the moment.Host an event
You're one step closer to meeting fellow Atlassian users at your local event. Learn more about Community Events