In order to resolve this issue, please visit https://spotify.gg/replacements. In the input box, supply the SPOTIFY Email that got downgraded.


For any possible issues, please check out this posts:

The family you tried to join is full

https://spotifygg.freshdesk.com/support/solutions/articles/47000456907-the-family-plan-you-tried-to-join-is-full 


This email has already been replaced or lost your replacement key

https://spotifygg.freshdesk.com/support/solutions/articles/47000455647-this-email-has-already-been-replaced-or-lost-your-replacement-key 


In case that you get any issues with this, please contact the online support or head over to https://spotifygg.freshdesk.com/support/tickets/new to open a ticket.