I think, reading a little bit between the lines, that your dc has an issue that doesn't have a formal diagnosis?
That is the root of all the problems then. They think you are making it up.
So to conteract it, you need professional support, and evidence eg your physio.
Then I would ask for a meeting, not with school, but with a wider group, not sure how you do that, you may need some help eg from parent support group. School, SS, health etc and lay out your concerns. X and Y professionals agree there is a problem, not having a diagnosis doesn't mean there isn't a problem, and then ask the school to respond.
Take notes at that meeting too.
The business about you not talking to other parents is just nuts