Help with my son being turned down for PIP

hi my son was diagnosed with speech learning difficulties. When about 4 , he didn’t speak till he was around 10 had speech lessons , deaf in one ear. So many tests etc but never given an exact diagnosis. We were told by Ed psych he would never live in his own cope etc etc. At primary school I was made too pick him up take him home for lunch etc, asked how does he eat, at one occasion. My husband and I fought too keep him in mainstream school. But we’re made too send him too special school.we were told he was delayed in his learning. 
If you met my son now26 he is clever very kind young man. 
But even tho he managed too come through cancerat 26 stage three. 
And went too college with extra help and then too uni I took him every day spoke too tutors took him too class. He suffered severe depression after father passing, was suicidal. Needed extra help too pass uni. 
I take him everywete he can’t sort any matters over phone struggles explaining himself cannot travel on his own. Or sort out problems. 
Theyy have totally taken his pip off him. 
So all his life he’s been told he has speech learning difficulties. And lives with me at home. 
I felt the pip review was talking about another person. 
He had no money coming in , as can’t cope with getting job etc. 

What can can I do