First, make sure that the time you dialed is normal working hours.
There are not many customer service staff on websites like this, and few people answer the phone.
Also, the phone number is wrong. You can ask the teacher for a special telephone number.
Xuexin.com:
Established in 2002, China Higher Education Student Information Network (chsi for short) is sponsored by the National College Student Information Consulting and Employment Guidance Center and undertaken by Xuexin.com Xue Xin Consulting Service Co., Ltd., and has opened more than 20 e-government systems and social information service departments. In July, 2004, the Ministry of Education issued the No.25 Teaching Announcement, taking Xuexin.com as the only designated inquiry website for higher education diploma in China.