I'm unsure why your original code is not working. However, if you want application-local broadcasts, you might want to use a LocalBroadcastManager instead of regular cross-application broadcasts.
Use this in your service:
LocalBroadcastManager.getInstance(this).sendBroadcast(intent);
and these in your activity:
LocalBroadcastManager.getInstance(this).registerReceiver(receiver,
new IntentFilter(NotifyService.NOTIFICATION));
LocalBroadcastManager.getInstance(this).unregisterReceiver(receiver);
Let me know if this changes anything. Again, I don't see why your original code doesn't work, so this is more of a guess.