Others stole my mobile phone number to send text messages.

Maybe your number was stolen. After this happens, you should immediately go to your own business hall to handle the card replacement business. If this situation still occurs after the new card is reissued, you should call 100 10 Unicom customer service to make a complaint.

Another possibility is that there is now a software that will specify that a certain number will be displayed on the mobile phone receiving the short message when sending it.

Maybe they set that number as your phone number, which is malicious. They can complain to China Unicom or call 1 10 to call the police.