Possible solution
kRMQQ,
I feel for you, almost everyone has been burned at one time or another in HK
If you have days off and are prepared to spend some time what I would suggest that you do is take the lens with you, stand outside the shop and tell every European who is about to enter the premises that these people are dishonest and you suggest they shop elsewhere
I guarantee that you will be threatened by the staff but if you stand your ground for a couple of days I would think that you might find that they are far more likely to refund your cash for the lens
Good luck