I agree with Polarbear EXCEPT that for now, you only have his side of the story. If you can verify that the teacher is knowingly forcing him to do things that are painful do to the disability, that's one thing, but I'd do a bit of sleuthing and educating first.
I agree you will want to verify that what your ds told you was what happened. The best thing to do would be to stop by after school today and talk in person to the teacher - *if* you feel like you aren't upset and can do that rationally etc (which I probably wouldn't feel like doing - actually usually didn't feel like doing on days like this, which we absolutely had quite a few times over the years). Sooo.. second best thing, and also just a good idea in general when you communicate via email is to restate what you understand happen per what your ds has told you - "My ds told me that...." - you can add "please let me know if there is a miscommunication or misunderstanding"... restating what you understand gives the teacher (or whoever is receiving the email) the opportunity to explain what happened from their perspective. You still might not know *for certain* what happened - we've had instances in negotiating through IEPs etc with our school where I would restate what I knew without a doubt was said or happened at a meeting in a follow-up email, only to have the school staff claim it never happened - but the important thing is, you've given an opportunity for the teacher to explain and you've also communicated what you were told happened. My gut feeling in the situation Happily described above it that I'd trust what my ds said happened.
This is really tough stuff - it's not easy knowing how to move, when to not move, what to say, who to take it to, etc. There aren't any clear-cut answers for any of it, no specific set of guidelines, each child and each teacher and each situation is different. You're doing a great job - it's just tough, and it's just a very bumpy road at times. You'll get there - keep trusting your own instincts and keep believing in your ds unless you're given a reason not to.
Re leaving a voicemail - I would send an email instead, because it is a written record of communication. You can refer back to it if things start to drag, and there are also state laws (and possibly school district policy) re when a reply has to be sent back to a request for a 504 or IEP eligibility meeting - so your email starts a time clock ticking. Granted, it should already be ticking and hopefully knowing what the deadlines are won't be an issue because the school will get that meeting going asap and it will happen this week and you won't have to worry about it. But just in case - I'd communicate things like the question about meeting status via email.
Hang in there -
polarbear