You are sending the same request code for your pending intens.
Change this:
PendingIntent contentIntent = PendingIntent.getActivity(context, 0, notificationIntent, 0);
To:
PendingIntent contentIntent = PendingIntent.getActivity(context, UNIQUE_INT_PER_CALL, notificationIntent, 0);
intents are not created if you send the same params. They are reused.