Fabian: I've ended up buying the 2nd hand Bose QC15's but i'm not happy with them at all. I'm not sure if i'm just too picky or that these ones have degraded or are even fakes.
How is the audio quality? If it's really, really bad then you may well have a counterfeit unit, particularly if the build quality also looks dodgy. They're actually quite common unfortunately. Did you buy from a reputable source?
If the audio quality is typical Bose - reasonably good to the untrained ear but falling short of Hifi quality - then chances are that you have a legit unit but have misunderstood the workings of active noise cancelling as per others' comments.
The more i listen with them, the better i think they are. The guy i brought them off has had 100% feedback on over 200 listings on trade me with his headphones. The bose ones are ex-airline but reconditioned and hence the reason for the cheaper price. I'm flying on thrusday and will hopefully see how well they work within an airplane environment. Will also take them into work and try them in the office. The quality of the music is heaps better than my other headphones so i don't think they are counterfeit. I have been trying to find a serial number on the headphones thou, internet said they are on the inside of the right ear cup but i can see anything.