Android : Notification click (Android)

I have one notification, created in MainActivity's OnStop(). It looks like that:

@Override
protected void onStop() {
    super.onStop();
    if (!finish){
        Intent intent = new Intent(this, MainActivity.class);
        intent.setAction(QUIT);
        PendingIntent pIntent = PendingIntent.getActivity(this, 0, intent, 0);
        // build notification
        // the addAction re-use the same intent to keep the example short
        n  = new Notification.Builder(this)
                .setContentTitle("Still working")
                .setContentText("Still getting data")
                .setSmallIcon(R.drawable.ic)
                .setContentIntent(pIntent)
                .setAutoCancel(true)
                .build();

        mNotificationManager.notify(0, n);
    }
}

It should reopen the MainActivity, but it is openning a new MainActivity, so I have two. What should I do for just open the same activity closed in OnStop()?