Hi Cudds,
Congratulations and welcome to the forum. On the assumption that you are also new to the site(please forgive me if you are not!) the following link should help you find your way around.
Welcome to Benefits and Work The fact that your letter tells you what to do if you disagree with the decision leads me to believe that it
is your decision letter.The ESA award is actually open-ended although it can be reviewed at any stage once 3 months have elapsed since the decision. This does not form part of the decision. For this reason claimants are not routinely notified when to expect reassessment but you can find out by asking DWP for the 'prognosis', you can also request a copy of all the paperwork associated with your claim. Whether or not you had a face2face assessment, the information in this link will be relevant.
ESA medical – what forms to ask for? If you have any further questions please reply to this message and we will do our best to help