That was exactly the case, but for whatever reason I got charged anyway. There was no code in the email itself, just a link. It's entirely possible that it doesn't register properly using Thunderbird/Firefox, and that's forgivable as it's not a deliberate con.
Understandably, I got a little resentlful when the first CS rep that contacted me tried to tell me I didn't use the link in the email when I know I did, and that even if I had done I wasn't eligable. This led me to believe they were making a false offer, therefore conning me. Either way, assuming the customer is wrong without question is a pretty crappy attitude to take.