While digging through my phone's memory to figure out why most of it had been used up, I discovered that Spotify had more than 8GB in use spread 50/50 between my phone's memory and SD card.
Why isn't there a way to tell Spotify to stop using the phone's memory? Things like this are exactly why SD cards exist - so we can use the phone's memory for apps and functions and the SD cards for media storage.
Have this problem too: When downloading (!Offlinemode is not working either, it keeps re-downloading every day, so infact - listen Spotify&Co....:Offline is not working. See link below). But at same time when erratically downloading for offline use, it fills my memory so the Offline-downloading spawns an "autosomal" stop of downloading due to Not Enough Memory. When uninstalling and removing all Spotify related files it releases about 8+GB of phone internal memory while it was using about 20+GB on my SDcard. Which I deleted. To try again. So I could try again.... etc etc.
This is also connected to issue described in WIRE about "Re-downloading" please see thread here.