Hi Mishcka and Welcome to the forum, you might want to have a look at the following FAQ which explain where everything is
Welcome to Benefits and Work I'm afraid that DWP has never been known for the clarity of their communication! The claimant is not routinely advised as to when the next reassessment can be expected, so that is no help either.
I'm afraid the only way you will know is to contact DWP and ask whether this is a decision letter or not