Hi9 tablet - internal storage almost full

Hello Everybody, On my HI9 tablet installed base apps (fb, chats, bowser) , without any huge background data’s. No photo and video, and the storage almost full 52 GB! (at 53GB). I analyzed storage with the file manager app, no big app and files. If a totally add all of the file size i calculated less than 4-5 GB. Have You any idea what/ how can android eat my storage?
I ran system clean and optimalize prog.
What can I do?