12306 sent 999 and didn't reply. What should I do?

In addition to the "signal problem" and "system problem" mentioned by others, this method may be used to solve it:

Check whether the SMS sent by your mobile phone by default is smart SMS. If it is, turn off smart SMS and replace it with ordinary SMS. I tried it myself, hoping to help you. )

The following is the flow chart of my experiment:

First, I sent four smart messages (in blue), but there was no response. After that, I sent a message by ordinary short message (white on black background) and got a reply immediately. (You can compare the time. A minute's reply to the text message should be an error message. )

In the second picture, I sent another ordinary short message and got a reply immediately.

Then I tried to change the SMS mode (smart SMS and ordinary SMS), and the results were the same:

Moreover, from the network state in the figure, it is found that whether the information can be replied has nothing to do with the network state (whether WiFi is enabled or not, whether 2G is enabled).

This is just one of the situations, and it does not rule out the situations mentioned by other interviewees. Please identify it yourself.