fb://page/{id} is the way to go:
final String url = "fb://page/" + facebookID
Intent facebookAppIntent = new Intent(Intent.ACTION_VIEW, Uri.parse(url));
facebookAppIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_WHEN_TASK_RESET);
startActivity(facebookAppIntent);
Are you sure you are using the ID number of your Facebook page and NOT the username?
What I mean is that if, for example, you want to open the Facebook page of Facebook itself (i.e. https://www.facebook.com/facebook) you have to use:
fb://page/20531316728
Since 20531316728 is the ID of the Facebook page (while facebook is the username).
If you don't know the ID of your Facebook page, you can retrieve it opening:
https://graph.facebook.com/{username}