The calling number is China Telecom, Heze, Shandong. Why is it empty?

The other party is using an Internet phone. The calling number is China Telecom, Heze, Shandong. The callback is empty, which is caused by the other party's network phone. The VoIP phone randomly generates a mobile phone number, which does not exist and the callback is empty. An empty number refers to a number that cannot be connected temporarily, or the dialed number has not been registered by the telecom service provider.