If you have the possibility of somehow contacting this teacher by email and get him to explain by written why did he fail you and you get him to write exactly what he told you or something similar, anything that comes across as discriminatory, I would say you have enough proof to sue the school for discrimination against a disability. I wouldn’t even sue the teacher as an individual, but the entire institution that he represents, because this incident tells me that the school doesn’t have a clear guideline against discrimination. Now, I am not a lawyer, so I don’t know if it is best to first take it to the HR area of the school or if it is better to take it straight to court. It would be worth it to get the recommendation of a professional. But either way, either HR pays you to shut up about it and not take it to court/social media/any platform where they could have something to lose- or the court demands a compensation for you from the school. But either way, it is time for these people to learn that discrimination is real, and so are the consequences of that just as well.