When calling back, the number that sent the message no longer exists.

There are two reasons. First, the other party's mobile phone made a call transfer and transferred the call to an empty number. Second, there is something wrong with the network or the number stored in the phone book is incorrect. Third, the other party's phone has set the dialed number as a blacklist.

Empty number generally refers to the number that has been recovered from the cancelled account during the freezing period or the number that does not exist or is not enabled. Call to prompt the empty number, which may be that the other party has set the call transfer to the empty number.