Obviously, I didn't answer the phone. Why did my call back become an empty number?

This situation is also possible. \r\nThere are several possibilities for calling and prompting "Phone number is empty": \r\n 1. The called party uses "call forwarding" to transfer its number to an empty number; \r\n2。 The called party uses the incoming call firewall to blacklist the contact person; \r\n3. The called party uses VoIP or number change software. \r\n* You'd better not return that ringing phone call. It could be a fraudulent phone call.