Why can’t I turn Spotify off?

No worries, you can deactivate that option by going to Settings > Notifications > Find Spotify > Disable show in the lock screen.

How do I stop Spotify playing on my phone?

How to Stop Spotify from Automatically Playing – Android
  1. Open the phone’s ‘Settings’ menu.
  2. Tap on ‘Apps’ setting to open it.
  3. Scroll to find ‘Spotify’ and tap.
  4. Then find the ‘Battery’ setting.
  5. Disable ‘Allow Background Activity. ‘