How do I unlock more levels?

Exactly!  You can no longer play on king.com because it ends at level 2825.  So from now on you can play the game on Windows 10 and also you probably weren't getting the challenges/events which you can now participate in.

Thanks @firebombmarkus.  I used to get quite a few messages in the old community asking why their game went back to the old version.  So we always directed them to a blog on how to get back their progress back.