-Tetsu-

Documents & Data, in my experience with iPhones, relates to your email/browser/messages cache (memory) that accumulates, along with other apps that require to actually go into the app settings and clear them.

This might help you out.

https://www.howtogeek.com/191264/how-to-free-up-space-on-an-iphone-or-ipad/

I'm surprised that the iPhone storage that says "Other" was not the culprit, as many people have been reporting a huge bug with IOS 11.0.3 and the Music App, leading to a corruption of music files and the application itself.

Did you delete them from the phone itself or iTunes?

For future reference, this might help. 

https://support.apple.com/en-us/HT204343

Working at the Genius bar for a year taught me some stuff lol

I looked up the data section in settings and there wasn't anything listed bigger than 900mb (well, that was line because I've saved a lot of gifs in Keep) and all other apps were below 300mb, didn't make up more than 10GB overall ...

The only reason why I deleted all music was that I've got a new computer and wanted to put some new songs onto my phone, which would have deleted all the music I've saved via my old computer anyway (that shit sucks a lot...)

well, had to reset the phone a few times because it lost its connection to my computer while updating to ios 11.03 (i was still running on 9.xx until this morning) and now it won't stop messing everything up...
first it told me I have about 18 MILLION TB on my phone, like what the fuck? (it showed the same amount of data on my computer too...)

reset it again after that, because I coundn't do anything ... it always told me storage is full and reset all settings after I changed them ...
and now it lists each song as an album when I open up the music player ...
but that problem with data is gone now, after the third reset, my storage is completely empty finally.

the only thing that's still bitching around is the music player with that album shit. I've started to transfer my music with "CopyTransManager" now and it seems like it's working a lot better than with iTunes... at least it's not listing each song as an album anymore ...

I really don't know what the fuck is wrong with that damn phone, I just don't want to reset it again haha ...

In that case, you'll need to delete the Music App entirely, and then download it from icloud.

You may have to reset your phone again though .

and you haven't even upgraded to 11.0.3 yet lolol.