In changing country to Canada from US one needs to input a new - Canadian - postal code. Spotify does not recognize it and I am therefore unable to change countries.
UI for this app is simply atrocious.....
Apologies for the late reply, but maybe I can still help :)
Have you tried to use an incognito tab, clear the cookies of your browser and use another browser or device?
When this doesn't work, you should try to use another internet connection (e.g. cellular data instead of WiFi).
Have a nice day!