My son has CP, and was refused mobility part of PIP. He's definitely entitled. What should I do?

Hi everyone 

Having seen the posts on the Pip My son too has cerebral palsy left sided hemiplegia.He was refused the mobility part scoring zero .he told them over the phone assessment that he cant go out alone due to social anxiety. He cannot plan a route of a journey without been accompanied by me his mam .and when we do go on public transport my son has a tendency to stare at people without even been aware of it which is also a safety issue .He has to be prompted he is staring .He finds been in crowds ,on the street in supermarkets very overwhelming. Yet the decision that they made was he could. My son also became emotional while on the phone during the assessment as talking about his disability effects him. Yet they said he didnt appear to show any anxiety during the call which was not true .what makes me irate is who are these ppl that make these decisions .the decision they made regarding my son were so totally inaccurate.now I want him to appeal .but he got upset today upon receipt of this letter .
My son is 27 .he does not go out to anywhere without been accompanied by me .he wont even go to the corner shop by himself .I have seen so many other ppl were also refused from posts I've read here .is it worth to appeal this decision .or is there say the final word ..this is totally disgusting .they are making such inaccurate assumptions and are they even aware the effect of their decision making it has on the individual .I'm really disgusted .my son has always received the living opponent of pip .they refused him mobility the first time and a friend told me to apply again for him as he definitely is entitled to it .I'm at a loss as to what to do now .