I've actually had this happen before - a couple of years ago I purchased a book which I couldn't download. Kobo offered me a refund back then but (why is no one going to be surprised about this?) then they "forgot" or something...
Anyway a week or so later the book was there so I gave up asking about my refund and I downloaded it. I assumed that they hadn't processed my refund because they fixed the book. Then a few weeks later of course my refund was processed. Because I am far too honest for my own good I actually attempted to explain to kobo that I needed to pay for the book as it had been fixed and I had downloaded it. You can imagine how successful that was! Eventually I gave up and figured I was owed a free book for all the problems I had experienced.
This time I got the book from the library so it didn't cost me anything. As I like to reread I thought I would buy it next year sometime (when it was nice and cheap to start with and with a good coupon I might even get it cheaper than the $4 I paid) so right now I really don't care whether they refund me or not.
I just wish they were a little better organised and there was someone in customer care who knew what was going on ...
Edit: PS melmac I hope you can download it soon as I really enjoyed reading it!