I recommend reaching out directly to Spotify Support. With this anonymous online contact form, you can reach them without subscribing to / having access to a Spotify account or the email that was used to create that account.
They can also be reached through their Twitter Handle @SpotifyCares
If you use the online contact form instead of Twitter, make sure to check your inbox and junk folder for an email from Spotify.
Hi. You should get in touch with Spotify via their Twitter page (@SpotifyCares), or by following this link: https://www.spotify.com/about-us/contact/contact-spotify-support/ . Afterwards. please check your inbox (and spam box) to check for their automatic reply. Once you get it, please reply to it immediatly (even if it's from an no-reply e-mail addres) to make sure an Spotify employee will get back to you as soon as possible. Spotify aims to reply within 24 hours.
Explain the situation and include as many details as possible, such as; Spotify will need to verify that you're the owner of the account.