Thanks for the reply. I believe you that it was a genuine mistake - as I said last night, you're still advertising the GF6 as a pre-order, two months after it was released. (You might want to look at that too, but for business reasons, not legal ones)
However, your explanation is still a little wanting. In one of your replies you said "Firstly I can confirm that this promotion had ended on June 1st". The advert was still running on the 30th of *July*. You say "As soon as we realised this mistake we removed the offer from Google" - actually, you seem to have removed that today, after I complained to the ASA. (Thanks for removing it, btw, although that seems a little silly now that the offer is back)
If I were you, I'd check your AdWords procedures. You're obviously making AdWord buys with old, no-longer-valid ad text. Also, the next time that a customer makes the effort to tell you that you're running ads for offers that don't exist, you should consider "Thank you very much for bringing this to our attention. We'll take steps to rectify it immediately" as a response, rather than telling them that they're seeing a cached web link even after they've supplied you with a screen-shot showing it's an advertisement.
Finally, "Im sorry you felt misled by the advert you saw" is a weaselly apology. How about "I'm sorry that our advert misled you"?