I have a very similar problem. Purchased from private seller on Craigslist; when I did reset - list was in Chinese. Discovered Model # is G900F, android version 4.4.2. Went ahead with factory reset but did not help storage issue. Added my bank app and now cannot download anything else (insufficient storage) Moved everything I could to 64gb sd card; same problem. Even went into app man and manually deleted all caches. No change. Downloaded a small cache cleaner and ran it; no change. Finally went in to "all" in app man and manually added up all memory used. Sure enough it is nearly 16GB without additional downloaded apps. There are a boatload of small android files (4KB and less) If I look at "downloaded" column in app man, the apps do not add up to the 14GB used as stated, leaving 572MB free. I wish I had kept my S3!!!! Although I have never felt the need before, I wonder if rooting is the answer. If it is, what mod would you recommend?