ok, now we have to factory reset it to rule out the firmware as the cause.
But first we backup your data onto the computer so you do not lose it.
To do this, download Kies from my link below onto your computer and install it.http://www.samsung.com/uk/support/usefulsoftware/KIES/
Once installed, run it and connect your phone to the computer.
Then perform a backup of the phone onto the computer.
Once completed successfully, disconnect the phone from the computer.
Then on the phone go to SETTINGS, then select PRIVACY, Select FACTORY DATA RESET then Select RESET PHONE
If you do not see it check under STORAGE instead of PRIVACY.
Let this complete and when it has, setup the phone again. Then connect the phone to the computer, open Kies and restore the backup you just did, to get your data back on the phone.
Let me know the results please