Urgent advice please

a while ago I wrote about my autistic son going for assessment, and I as his appointee going along with him.
The 'assessor' (who later admitted he was a paramedic, who knew nothing at all about autism) insisted my son answer. I explained that he was unlikely to get any accurate information from my son, and that is why I was there to act on his behalf.

Despite my constant need to interject because my son was offering stock answers (question: do you have any pets? my sons answer: no. we do in fact have three dogs, two cats and several chickens!) and clearly guessing at mental arithmatic questions, being way of mark with answers, which took him at least a minute and a half of stuttering before blurting out an (incorrect) answer!

I had to pull the assessor up on a couple of things and at the end had to make him go back and correct something, which I had tried to address earlier and he had said 'we'll come back to that' but didnt, instead, coming to an erroneous judgement off his own bat.

Having filled in the forms against their own descriptors (I worked out my son had a total of twelve), I was shocked to learn her was turned down - saying he only scored 2! I asked them to look at it again, and gave my reasons. I had the decision this morning that they had looked again and he still only had 2!

I am furious on my sons behalf and want to appeal, but I am at the end of my tether, suffering from and being treated for clinical depression and anxiety myself (perhaps I ought to be claiming for myself too!), and I am not sure I have the strength. I have spent the whole of my sons life fighting for him, I am so angry and upset.
I know thousands of people with autism are in the same boat - my son other than his autism and associated problems is in rude health, but i desperately need help. can anyone point me to someone who specialises?

many thanks

DC x