Why do mobile phones automatically send messages repeatedly?

Poisoning or downloading malicious software.

The message sent doesn't show that it was sent successfully because there is a problem with the settings. Just modify the settings.

Poisoning or downloading malicious software can repeatedly send short messages to defraud the short message fee.

Use anti-virus software to see if there is poisoning. If it is poisoned, just clean up the virus. If it is not poisoning, see if you have downloaded some vicious third-party software that is not genuine. If so, delete it.

If the above two conditions are not met, you can try to enter Settings-Application Manager-All-SMS-Clear Data/Clear Default Settings.

If it still doesn't work, I suggest you restore the machine to the factory settings, as follows: Setup-Reset-Restore the factory settings (but since this machine will lose all data in the mobile phone when it is restored to the factory settings, I suggest you back up important data such as phone book, video and pictures in advance).

Or download the firmware and reinstall the system, and make a backup, or go to the service center for processing.