Sisunlondie,
So sorry to hear about exam problems with your son.
I am mum of the child with ASD too. My son got grade 3 on mock exams in English.
I understand your frustration but you need to find a strategy.
Our top school did not give too much what required for my autistic child. The method offered by the school did not work. We took a tutor who has great experience with SEN children ( ASD/ADHD).
Together, we calculated the time, the order of questions, when should to get a break, told to ask for help to clarify questions,
We learned to split questions making them easier ( finding key words). We looked at different structures of the text.
We taught to make a plan ( putting important words in brackets). Then, get a short break and start to expand every step of the plan.
It was not clear a lot of things at the beginning . My child could not even to separate paragraphs.
Exam techniques offered by the school for analysis still like jungles to him.
In fact, when child finished Literature exams, 85% of both papers were skills given by his tutor, from YouTube channel Mr Everything English and at home.
I am sure, you also can manage that, you still have a time to get a strong pass.