You would probably want the credit for the Conrad stay. It should get you more points than the HGI. Do you have anyone travelling with you who might benefit from the stay/night/points? You can try transferring the reservation to that fellow traveller but name and payment of reservation has to change as well. At the very least, cancel the HGI even if it gets you nothing back except maybe avoidance of a potential headache as you try to sort things out with Hilton.