Here is a full list of all applications installed on the device:
I have already used Battery Doctor (and other apps) and cleaned cache. So what is 7.2 gb used for? How can i clean it?
I don't know if it can help but the phone was already in use before.
Update: Settings -> General -> About screen:
Best Answer
Looks like that iOS is taking some space since it says the capacity is 12GB even though (I'm guessing) your device is 16GB.