Obviously, businesses do this a lot; making the refund process obtuse and giving you an easy way out that just so happens to save them real money. If they had to pay back every subscriber, it would go from possibly a mild disappointment to an actual dent in their bottom line.
I found my email in the spam folder, it had a totally different sender and even a different title from the previous mail I had received from the mag (way back a year ago when they announced issue 4) but nonetheless, the code provided works in the website.
Can't say the mag was that exciting, but I guess I better find the 1st 4 issues I have packed away and store them properly, could be something to have in the future.