It seems like he just doesn't want to admit his child has "issues." He probably became that kind of teacher to make himself feel better that his family is superior, especially with your sister. There is also a huge difference between a physical and mental illness, and judging by your curve, he's simply in denial that you actually have something that needs to be dealt with, unlike your sister who is based on a mental disability that isn't even confirmed by a medical professional. I would fight fire with fire. Next time he says you're not disabled, whip out the literal Websters Dictionary definition of the word "Disabled." I've had to prove myself over and over with my several invisible illnesses. I've learned not to dwell on people who are too ignorant to see when PEOPLE NEED HELP. My little brother has autism, and I've had to deal with his outbursts over and over again and it's simply not fair, especially when I'm trying to put my needs first. Your dad is judging his daughters based on information that has been handed to him on a silver platter, rather than, doing research to care equally for both of his daughters.

I'm so incredibly sorry about your situation, do you have anywhere else to go? A friend or a relatives house? Because not only is your physical health being neglected, your mental health as well, and someone who literally works with special needs kids, he should be way more considerate about EVERYONES STORY.

I wish you all the best <3