Remove the SIM card from the iPhone
Go to Settings
Tap Cellular or Mobile Data
Select the SIM line
Tap Delete Cellular Plan if available
Confirm deletion
If using eSIM, go to Settings
Tap Cellular or Mobile Data
Tap the eSIM plan
Tap Remove Cellular Plan
Confirm removal
Remove the SIM card from the device tray
Restart the iPhone
Sign out of iMessage if needed
Sign out of FaceTime if needed
Remove the number from Apple ID trusted phone numbers
Remove the number from Contacts if saved
Contact your carrier to deactivate the SIM number permanently
Ask the carrier to cancel the line
Request SIM deactivation and number termination
Factory reset the iPhone if you want all data removed from the device
Erase all content and settings from Settings
Do not insert the SIM again