While credit card fraud is massive and legendary here in Thailand, based on the detail you provided my guess is that you're dealing with new/untrained staff who were having trouble running your card - is it Thai or foreign? - and so they had twelve staff standing around, texting the boss, kept failing at the authorization (the 6 tries), gabbing back and forth, maybe they needed their store PIN, but got confused and asked you for a "PIN"?
I'd chalk it up to incompetence/language rather than attempted fraud, but that's just my best guess.
EM Quartier is very Hi-So, I felt like my bank balance was being drained as I walked through, just as an entry fee. Even middle class locals get a chuckle out of the place - I was at a funeral/wake recently and a group was talking about how, for lack of a better translated word, pretentious it is.
EM Quartier is a new mall which opened at Phrom Phong BTS on 27 March 2015, and is part of The Mall Group's empire (they also are revamping Emporium across the road).
http://www.theemdistrict.com/index.php
I guess The Helix is the name of the food area?
http://www.theemdistrict.com/dining-group.php?id=1 (load more to see all).
Emack & Bolio's, someone must have gone to MIT or Harvard? I've seen an E&B in Central World too. Amazing given that all Thais are lactose intolerant.
They also have a Croissant Taiyaki which is all the rage now - and pretty good.