Sounds like you might have opted out of sharing your data with Facebook. You can check this on your account page here. You should also make sure that on Facebook's end here, Spotify has to be allowed to have access to personal data.
Unfortunately at this time it is not possible to change an account’s username. The closest you can get is to link your Spotify account to your Facebook profile again so that your Facebook display name is the one shown on your account.
If you are really desperate to change your username, it is possible to create a new account!
Hope this helps and have a nice day!
Jose_MRock Star 10
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