Okay, this has happened to me three times where the Spotify app (android) thinks I'm offline when I'm not. I have a Samsung A5. I have tried logging off, logging in with a username and password, logging in with Facebook, uninstalling the app and reinstalling. What worked for me was to go into the Settings on my phone, under Applications, finding the app, and telling it to "Force Stop". "Yes" to the message about potential errors. Going back into Spotify and it works! I'm online again! It's very annoying though, for an app I'm paying monthly to use and it doesn't always work.