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

what kind of visa are you applying for? Common tourist visas, student visas are not accepted, and the immigration office has a public hearing time. It is normal for no one to pay attention to you if it does not exceed the normal hearing time. If the time exceeds, 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 help you check it. In addition, student visas from outside Australia are not handled by domestic embassies. If you submit your application in China, you should consult the Adelaide Student Visa Center.