If your account was created via Facebook and you deactivated your account, I'm afraid you won't be able to see your Facebook display name as your Spotify username. 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 🙂