In all it sounds like they are just trying to coerce u into payment thru a lawyer's letter.
To be honest , if they could have done something much more substantial they would have done so already since it's a full decade. Most likely is they have just really ran out of targets and now targeting the database of old customers.
To end this once and for all, I'll seek a lawyer'a advice , if monies is a problem - seeking your MP for help (free legal help) may be another avenue.
I was once stuck for 4 hours in a room with my gf (for the promise of a $50 Isetan voucher) when I was still an Uni student and honestly their tactics really disgust me.