Apologies I was in a rush & didn’t lick up the whole story.
You can realistically only take it to the next stage if there was a breach of law, get some advice. Id gather all your paperwork then speak to Fightback they can advise you fully. I would not advise going further without professional help.
Your other option would be to trigger a reassessment by notifying the dwp of a change in disability but again seek advice before doing anything as you could end up losing the entire award if not careful.