The very least you should have done, is looked at the manufacturers spec’s for that model, which can be found in the online brochure, rather than listen to a salesman. However, it could also be said the salesman could have pointed you to the online brochure.
You could try and explain to Motability, that the salesman didn’t mention mention everything that was missing, of which some is of upmost importnt for your condition and when you asked the salesman to view the car, the interior was wrapped up from factory so it was impossible to tell. Saying you didn’t bother test driving because it was the same car won’t bode well!
I don’t hold my breath if I’m honest, but its worth trying.