It’s not unusual for schools to ration AP courses. Sometimes there just isn’t enough room in the class for everyone who wants it. We don’t have enough information to know why others got this class and you didn’t. Maybe they went by grades in prior classes, maybe by teacher recommendations, maybe it’s random. We just don’t know.
Sometimes you just don’t get what you want even if you make a lot of noise. It sounds like you’ve emailed and called and haven’t gotten a response. Could it be that whoever you are trying to contact isn’t in the office over the summer or is on vacation? I’d wait until school starts and go see your guidance counselor in person on the first day to see if you can find out why. But, it may be that the class is full and nothing can be done.