There are two things I would do if I were in your place - first, I'd want to have a copy of each test and as many of your ds' homework assignments (graded) as possible. While it's possible this is entirely a bad teacher fit, you also have mentioned your ds wasn't accelerated in math this year and you had to request it. While he had high test scores at some point in time and a comment that he should be capable of working ahead of grade level, that was several years ago (if I understand correctly), and that was also before he was attempting a higher level of math. I would want to be sure that I understood whether or not there are challenges for my ds related to the actual work.
Second thing is request a classroom change. I suspect there is no way you'll be able to turn around the relationship with this current teacher.
One other note - back to your OP where you noted your ds reads calculus for fun at home - just fwiw - I have a 2E dd who is challenged in reading (different challenge for sure), but fwiw, she reads much higher level books at home than she does at school and she enjoys them. BUT she's not taking in the content of those books the way she needs to to be successful in school. I only mention this because I think it's quite possible your ds might be able to read and enjoy higher level math at home, but still not be at that ability level for problem-solving.
It's tough sometimes to see the full picture when a teacher-student relationship is such a poor fit - we have totally btdt with one of my ds' teachers (although at a much younger age). My only advice in hindsight is to try to deal with the teacher as one issue but also don't ignore that there might be something real going on with math (lack of interest, lack of motivation, not as highly able as you had hoped, some type of challenge, whatever).
Best wishes,
polarbear
