I'd try to move on as best I could and have as little or no interaction with the school as much as possible. I have a 2e/pg 7.5-yr-old son and had 'issues' with the public/private schools too, though not quite like yours; and I'm now un/homeschooling as a result. I'm so sorry to hear what happened to you and your child. That's totally unacceptable and very upsetting imo.
I would try put my energies into providing the best ways my child could foster and learn at home. If this means going outside the box and being unconventional with learning, then so be it. Your child will be better off.
I'd also say to re-direct your anger to forums like this and others and consider being an advocate for 2e kids, school reform, and un/homeschooling. That's what I did and have done. It helps. Things aren't going to change unless we start to get our voices heard.
As a parent, your job and priority is to ensure your child's welfare and safety and to help him receive an appropriate education. No one will be as invested or motivated to educate your child as you. That's something to always bear in mind.
