Well, your situation really stinks, but as you stated, this was your responsibility and the hotel did nothing wrong (how angry would you have been if you showed up at midnight to check in and your rooms had been given away?).

You really don't have leg to stand on - the payment you are making is actually a no show penalty, not a room charge so technically you're not entitled to any points. It would be a nice gesture for the manager to give them to you, but it would be just that - a nice gesture, not an obligation. Your anger belongs with the person who forgot to cancel the rooms - an expensive lesson learned.