8 year old son to have no contact with his best friend at school

Hello all,  I am new here and looking for some suggestions as to how we support our recently diagnosed  (Aspergers)8 year old son with a difficult situation at school.  He has always struggled to maintain friendships and has been bullied by older children at his school for having a facial tic.  In September he made a good friend with another boy in his class who was willing to be his buddy in the playground and at lunchtimes.   Last week our son was taken to one side by his class teacher and told that he was no longer allowed to play with this boy or have him as a buddy/sit with him in class.  No explanation was given and since then he has refused to go into his classroom and is experiencing bad meltdowns at home and is unable to sleep.  When I asked the class teacher why the school had taken this decision he explained that the boy's parents had requested that their son be kept away and was to have no contact.  The school will not tell me the reasons why (apparently they are confidential) and the whole school staff have been informed. Even the class teacher says that he has no justifiable concerns about the two boys being friends.   Our son is distraught at the decision and feels he is being treated "worse than bullies"  He is feeling anxious and embarrassed and is isolating himself away from his peers by working in the SENCo s office for most of the school day.  The school will not back down on their decision and seem oblivious to the distress this is causing our son. Any advice on how we should handle the situation or help him move forwards would be gratefully received! He refused to go to school at the beginning of this year when he was being bullied and my biggest worry is that this will trigger another episode of school refusal.  Many thanks Sarah