However, I have managed to change it a couple of years ago because before moving to Spain I had been listening music through Spotify in Finland since it came available.
Now, when I try to replace my Spanish credit card info with my current UK card it's not letting me saying that the credit card must match the country setting. The country selection is greyed out in the 'Edit profile' screen so I can't change it there. (And by the way, the post code was still the Finnish post code from years ago and that didn't seem to matter.)
Why is it not letting me change country and credit card details now while it obviously was possible before?