I read somewhere on here that it was HK law that the CC needs to be shown at check-in on ex-HKG itn. When you book awards ex HKG on the QF website it comes up with an extra page in the process warning you that this is the case.

I have flown ex HKG (most of my HKG flights are part of a bigger itn not originating in HKG in which case it is not necessary to show the card) and I didn't have the CC. The staff were able to use a different credit card to verify the details matched.

You could try ringing CX and asking them what you need to do now you don't have the card anymore.