Still no luck...called again this afternoon and it initially looked positive as the agent I spoke with said he was able to see and confirm availability...but when I checked my itinerary online he had only added the waitlist for business class and not the confirmed coach seat. Called back and asked to add the confirmed economy award on that flight, and was initially told again that there was no availability. When I said that I was looking at the website and it said there was, I was queried about whether I was sure I was looking at the right date, looking at award instead of paid inventory, etc. Then I was put on an extended hold, and when the agent came back he again told me that they do not see the inventory, what I am seeing is "online only" inventory and they have no way of booking it. I'm going to try the advice above to call the Singapore call centre when I get home from work tonight, but this is incredibly frustrating.