On the phone Check that the Dock Connection is Clean and Free from lint.
Close All Open Apps... Perform a Reset... Try again...
Reset ( No Data will be Lost )
Press and hold the Sleep/Wake button and the Home button at the same time for at least ten seconds, until the Apple logo appears. Release the Buttons.
If the issue persists then a Visit to an Apple Store or AASP (Authorized Apple Service Provider) is the Next Step... to have the Device and the Cables and charger evaluated....
Be sure to make an appointment first...
By trying different bales and different chargers I believe you have eliminated those from being the problem.
First thing to try is to reset your device. Press and hold the Home and Sleep buttons simultaneously ignoring the red slider should one appear until the Apple logo appears. Let go of the buttons and let the device restart. See if that fixes your problem.
If the problem continues it resides in the phone. First check the dock connector to make sure there is no dirt in there. Also make sure the cable connects securely to your phone.
If none of these helps resolve the issue make an appointment at at Apple Store to have you Phine examined.