If people around you on the same network have bars but you are stuck in SOS mode, the problem is specific to your device or account. First, check Settings > General > About to see if a "Carrier Settings Update" pops up; these are vital for maintaining tower compatibility. If your software is current, your SIM card may have become "de-provisioned" or damaged. It’s also worth checking if you’ve accidentally disabled your primary SIM in the settings menu. If all else fails, a quick call to your carrier from another phone can confirm if there is a block on your specific line.