Hi Diane
Unfortunately, Capita do not have to accept your request for a paper-based assessment.
You can ring and ask them to change your mind - however, if you do that, they may argue that you are capable of communicating over the phone! (I'm not saying it's the same - just what their attitude might be.
You can ring and ask what will it take for you to have a paper-based assessment - they might say a letter from your GP confirming that it would cause you "overwhelming psychological distress" - and that statement needs to appear in the letter if your GP is willing to write one. Even that is not always accepted.
You can contact your GP and see if they will get involved and see if they can get Capita and DWP to change their mind.
It is very difficult to get them to change their mind without specific support from a medical professional about your mental health difficulties.
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems