I can understand your frustration, but the way i look at it is that I enjoy my leons, they do what it says on the tin and as long as this issue doesn't cost me any more money now or in the future. ie higher VED or something similar, then I'm not that bothered and if I get a bit of cash back from VAG as way of an apology, that's a bonus ( not holding my breath)
VAG lied, Yes, but so do most companies- I bought some Lynx and im still waiting for scantily clad models to chase me across the beach-
Now i do admire your tanasaty,
But
There's a whole host of legal arguments/precedent why your unlikely too ever obtain a full refund of your 2014 purchase price back, unless
1. VAG decided to offer it out the goodness of their hearts - highly unlikely as they wouldn't want to be setting a precedent which could ultimately end in them fully refunding every customer effected , it would bankrupt VAG
2. Your a internet billionaire with unlimited
resources and several years of spare time on your hands to fight VAG for a refund through the court's and who would fight you tooth and nail to avoid losing (see end of point 1)
All just my opinion of course, but I wouldn't get too hung up on it, just enjoy the car, it still does all it did when you bought it and the roof for second hand vag cars hasn't appeared to have fallen in, so apart from the exhaust not being so clean as you though, what's the big deal