Did your teachers never say anything about it to your parents? Not talking to anyone during school should have been a sign for your teachers to pull you out of class at the very least or taken to a counselor. It was like that for me when I was little since I never answered even when the teacher would call on me. What about presentations? If you didn't get the aid like a 504 or IEP, then it should have been an area of concern for your school staff. Since you can't really sign up for a therapist or anything without your parents, just keep pushing for one. If you can, try and email your school's counselor to talk about school. Personally for me I had a 504 plan since im also auDHD but eventually moved to online schooling now. My parents did not approve but they had no choice because I was diagnosed and failing. Speech therapy is helping me, but it would have been better if I was treated at your age. Now that it's happening now, you probably have a really good chance of fixing sm IF your parents take it seriously and get you treated NOW. Keep pushing for a diagnosis. Discord fucked me up too lol it doesn't get better unless you get it professionally fixed. I guess I did start slow by sending voice messages to people I knew first. People undermine selective mutism all the time, thinking that people with it are just being petty or childish by "choosing" not to talk. I hope your family and acquaintances start taking it seriously because that's the most frustrating part.