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I have a few recommendations for this issue, first, if you havent already, I would restart the iPhone.
Restarting your device
- Press and hold the Sleep/Wake button for a few seconds until the red "slide to power off" slider appears, and then slide the slider.
- Press and hold the Sleep/Wake button until the Apple logo appears.
From: iPhone, iPad, iPod touch: Turning off and on (restarting) and resetting
If that doesnt resolve the issue, or you cannot restart it the normal way, then you can try resetting the phone.
Press and hold the Sleep/Wake button and the Home button together for at least ten seconds, until the Apple logo appears.
All the very best,