Hi @121538422!
Try reinstalling. It may move its default storage to the external SD card.
You might want to give kudos to this idea about bringing back the option to choose a folder for downloaded files on Android. More kudos will persuade Spotify to make the feature available. Also, don't forget to post your reasons on why should Spotify implement it in the comments section. Click here for more info about ideas in the Spotify Community.
Hope this helps 🙂