Help with kindergarten problems

Sorry this is so long: I’m dealing with some issues concerning my kiddos kindergarten teacher at school. It started with the teacher yelling at the class, to the point where my child would come home crying and not want to go back the next day. After this continued, I joined forces with another mom and she spoke to the principal, while I emailed the teacher. The response was dismissive—they said kindergarten is harder than preschool, and yelling is necessary to get the point across. They also mentioned the teacher has hearing problems, which we were never told about. Then, the teacher took away my son’s chair and replaced it with a stool without notifying us. I assumed it was to help with distractions, but when I emailed her, she just said he could get his chair back if he wanted. Later, my son came home telling me his teacher makes them call her “mom,” and once he even came home wet because she wouldn’t let him use the bathroom, despite being fully potty-trained. When I asked her about it, she didn’t apologize—she never does—and just said “he wasn’t that wet.” The final straw was when she left my son alone in the bathroom, and the entire class went downstairs without him. He found himself in an empty, dark classroom and had to ask another teacher for help. They eventually found his class downstairs, and again, there was no apology—just a comment that he should “hurry up next time.” I talked to the principal about all this, and she apologized for the teacher’s behavior, promising to address it. However, instead of an apology from the teacher, we got an email listing things my son is supposedly doing wrong. She even suggested putting him on a timer for bathroom and water breaks, claiming he goes too often—something we’ve never been told before. I’m unsure of what to do. I don’t want to pull him out of the class because he has so many friends, but the situation feels unfair, especially with the idea of timing even he has bathroom breaks and drinks water. Do you have any advice on how to handle this? Idek what to do