Impossible to free up storage/move to SD card

[7dude]

Device: Asus Zenfone Max

My phone has been complaining about low storage for a while, I found out that Spotify is using around 6GB. So I try changing the storage to SD card where I have 60 GB of free space, but the app only tells me it's moving the files, then does nothing. Okay, so let's delete it, right? Go to settings, clear cache, and then - still no more free space. Force stop the app, try to remove all data in app manager, uninstall... Anything I do I can't get more than 700MB free, and I can't find any place where Spotify stores those 6GB of music! It definitely isn't in /Android/data/com.spotify.music, that folder is empty right now after clearing th e cache, when uninstalled it didn't even exist. Help!

Also, now after clearing the cache the app tells me it's only using 8MB internal memory, but none of the space it used to take up is free. **bleep**