Please have a check with your service provider. If still no help, then try resetting the device.1.Power off the phone.2.Press and hold "Vol+", "Menu", and "Power" key until the phone goes to recovery mode.3.Use "Vol+" and "Vol-" to move the cursor up and down.4.Move cursor to "wipe data/factory reset", press "Back" key to select it.5.Now move cursor down to "Yes - delete all user data" and press "Back" to select it.6.The data will be erased.7.The cursor will be on "reboot system now" at the end, so just press "Back" key to reboot the phone normally.
WARNING: All user data will be completely cleared; the phone will be in a factory reset status.