How can I unsubscribe from iOS pre-releases?
Usually, the procedure for doing this is to delete the profile in the Settings app, then restart the phone. If you didn't reboot then it's possible that it still thinks you have the profile.

Make sure you have not accidentally allowed it to update to a beta version (for example 9.3.1) as it's possible that if you are currently running a beta version then you might still get the later betas.