Several users have reported that their iPhone 5 uses cellular data while the phone is connected to a Wi-Fi network resulting big overages charges. It seems specific to Verizon users and if you are experiencing this issue, you may need to update your carrier setting to resolve this problem. Please try this fix:
- Navigate to Settings > General > About
- Wait to see if any carrier settings update
- Tap OK to update, then turn off your iPhone by pressing and holding the on/off button until you see the red slider. Once you see this, slide to turn off.
- Turn back on your phone by pressing and holding the on/off button until you see the Apple logo.