It's true that a Premium account is required to link Spotify to Alexa. It's also a good idea to make sure that the country settings on both apps match.
Keep in mind that there's always a possibility that you may not be able to use the integration if our partner has not made it available in your country.
If you've never had Premium before, you should be able to take a 30 day Premium trial offer for free when you upgrade. Just log in and upgrade here. You can then try it out and see if it works for you. If you don't want to continue, you can cancel the subscription anytime.