Drunk galaxy j7+ storage
I'm going to assume you are referring to Internal Storage and not the SD Card, in which case it would be good to wipe all of it. More specifically, a reset of your Android. Before you do this, you're probably going to want to back up important files to a computer or upload them to an online drive.

Here's a link to a guide that will help you reset (skip to step 3): https://www.wikihow.tech/Erase-Internal-Storage-on-Android

Alternatively, if you're not willing to reset, then it may be preferable to delete every single one of your apps until you're at a point where you have lots of space. My Android is also really silly when it comes to evaluating remaining space: I check the settings and go to storage and it tells me I have 500 MB left, yet when I connect it to my computer it says I have 0 bytes of free space in internal storage.

It could also be a problem with the drive itself (a physical hardware issue) in which case the only solution is buying a new phone unless you're willing to go through the trouble of changing that one part (the drive). My advice to you: clear up the apps, the photos, the videos etc. until the storage can reorient itself. Just do a general cleanup, and then it should do a better job of telling you how much space is left.