Update:
Subsequent to our disastrous visit to the Mandarin flag ship store we were contacted by phone and asked to make a return visit with a meal for 2 on them. Suggested it was a bit too soon and suggested they email the verbal offer, that suggestion was refused.
Received another call two days later asking when we would return. We suggested it would not be until after Easter. Again told to just reserve and ask for 'Sam' when we arrived. Again suggested it was to soon and the bad experience was still too fresh in our mind.
We were told a letter would be sent that we could present when we arrived, that would confirm a gratis meal for two for lunch or dinner. Now April 20/18 and still no sign of a letter. This leads us to believe the offer was mear lip service and never expected to be taken up.
Sad really because their history was great but perhaps success has breed apathy from a customer service perspective.