You no longer have to send them an e-mail, you can use a contact form instead. In the first field, select 'Removing/Cancelling Spotify', in the second 'Delete/close my Spotify account' and in the third select your reason for leaving.
You can also send an email to firstname.lastname@example.org and provide them with your username, date of birth and postal code and they'll delete the account for you.
If you can't find any contact info and still wish to ask something, for example a question about what exactly is deleted, about data retention, etc., you may contact the domain owners using this info.
If you signed up for Spotify using a third-party login such as Facebook or Twitter, you probably want to revoke all access from Spotify. Click the icon below to find out how.