My device Storage is out of memory

image of my device storage My device storage (tablet s ) is full (16GB ) although the total size of all files and folders is much less (3 GB)][1] my tablet s is out of memory , the total size of all folders and files is about 3 GB and apps are not too many , just the essential ones ?

I have already used clean master app but it doesnt clean much just 300 MB