It must be wrong for your school to ask you to teach voluntarily, and there is no school rule to ask you to do so. Moreover, the environment in Xinjiang is really hard and prone to altitude sickness. But, to put it bluntly, your arms can't twist your thighs now, and you can't resist.

I suggest you communicate with the school first, can you not go or arrange other internships? If you can't, go directly to the local education bureau to complain or write a letter of recommendation online, or use the public opinion in Weibo to expose it.