One more update, this is a good one. I logged the issue with Amazon, they responded with this great email.
Hello,
I am sorry to hear that you are unable to access your Spotify account to your Echo device on the Alexa app. I appreciate your efforts for trying few troubleshooting steps.
Thank you for bringing this to our notice. I've checked and see that this is a known issue and most of our customers are facing the same.
This has been reported to our technical team and they are currently working on it to resolve it as soon as possible.
I've created a ticket for the issue you have with Case ID: 0094194228, I'm filing this information over to our Amazon Echo Development team to make your device works properly with your Spotify account. As soon as we have the update we'll let you know.
These errors are usually corrected shortly after they're reported.
Situations such as this are rare, and our goal is to help resolve any problems you encounter as quickly as possible and we always want our customers to be happy.
Be assured that once they make the necessary changes you will be able to access your Spotify account.
I will take the complete responsibility of this for you and I'm personally following this and will definitely get back to you as soon as I receive an update from my technical team.
Should you require any additional information or assistance before then, please do not hesitate to contact us via live medium.