Sim card is not working

Not enough information. Is this existing service or new service? Which iPhone do you have? Physical sim or e-Sim? 

Hello @Larysa,

We hear you, and let's get the help you need. 

We suggest the below steps which would help  

• If you're using iOS, tap Settings > General > Reset > Reset Network Settings.
• On Android, go to Settings > System > Advanced > Reset options > Reset network settings.
• Switch on and turn off the Airplane mode. 
• Also, if in case you have opted for e-sim and it was deleted. 
  • ⁠Go to your myAT&T account overview.
  • Scroll to My devices.
  • Choose Manage for the device that needs a new eSIM.
  • Scroll to Options & settings and select Get a new eSIM.
  • Confirm your selection to Get a new eSIM.
  • Follow the prompts to complete your eSIM setup.

Hope this helps! Feel free to revert for any further questions. 

Thanks for visiting AT&T Community Forums,
Gary, Community Forums Specialist.