Thanks for getting in touch with the Spotify Community. We'd like to help.
In this case, please make sure to follow these steps to connect your Spotify account to your profile Facebook.
If you're still getting the same message, check that you don't have another account created with your Facebook details. Try to log in with any other email addresses you could've used to create another account.
Let us know how it goes or if you have any questions. We'll be here for you.
Make sure you don't have another account associated with it. If you still can't get it to work after that. Talk to an admin about shutting down the account associated with your FB account so you can use it for your actual one.