Finally my system recognized the space used in the SD so in theory Spotify could be able reading the card, but it still doesn't. I contacted Spotify Support by chat and we literally spent hours trying to solve the problem, but we couldn't. We came up with even the most drastic solution such as hard reset, and that didn't help either. So in my case this issue remains unsolved. Possible cause (I think): My old Galaxy S4 running Android 5.0.1. Spotify worked well on this phone Before, but not anymore.