the seeker
My guess is that the information that you sent to the DWP was not passed on to the Assessment Provider and the DWP have simply asked the AP to arrange another appointment.
So I would contact the AP and send them the letter that your GP wrote for the DWP but make sure that it is unambiguous, that there are no comments such as "might suffer" or "could lead to a deteriorated condition".
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems