What lessons have you been doing?
lessons

Learn and apply the most important principles of chess.
Always blunder-check your moves.
Solve tactics in the right way.
Analyze your games.
Study games of strong players.
Learn how to be more psychologically resilient.
Work on your time management skills.
Get a coach if you can.

Start with the basic section and go from there. They can be fairly useful, but you have to start at the start. If you're asking why your rating doesn't improve from doing the lessons, it's because lessons have no impact on any form of rating (puzzles, live, daily, whatever).
Hi, I have a diamond membership and I have tried the "learn -> lessons" but I just cannot improve. Can someone help me how to best use the lesson features and what to expect. I watch the videos and then try to solve the puzzles but nothing happens. What should I do now?