I sent a reminder letter to the Australian Embassy for several hours. Why don't I even have an automatic reply?

What kind of visa did you apply for? Ordinary tourist visas and student visas are not accepted, and the immigration bureau has time for public hearings. It is normal for no one to pay attention to you if you don't listen for more than normal time. If the time is over, for example, the student has signed and submitted it for more than 3 months, then you can go to the immigration office to complain or consult, and someone will check it for you. In addition, the domestic embassy does not handle student visas outside Australia. If you submit your application in China, you should consult the Adelaide Student Visa Center.