If you haven't already, try restarting the router! :)
If that didn't work, I'd recommend checking the hosts file, maybe that address is simply redirected incorrectly.
1. open Notepad as an administrator (right-click - Open as Administrator)
2. go to File - Open and navigate to
3. Choose "All Files" instead of "Text Documents" next to the File Name box. You'll see a handful of files. Pick hosts and click on Open.
4. The file is opened. You will see a block of text with # in front of each line and might see entries like
0.0.0.0 website.com 127.0.0.1 website2.com
Check for any entries with spotify or fastly in the address. Examples may look like:
0.0.0.0 weblb-wg.gslb.spotify.com 0.0.0.0 prod.b.ssl.us-eu.fastlylb.net
(and any variations inbetween)
5. If you do find any, you can delete the line. You can also add a # in front of the line, that's 'commenting out'.
6. Save your changes. Restart Spotify.
You can also try removing all lines to see what happens.
This Wikihow article has some additional steps you can try (DNS settings for example).
Let me know how it goes :)