In the end, I took your advice and did write a review. Other people need to know. I took care to mention I was not commenting on the content of the book, but on the quality of the ebook.
Harry, it is not really about *my* problem. I just wanted to inform other people about what kind of service they can expect if they run into problems. And I want to boycott Waterstones, because if I don't, it's like I don't really care what their customer service is. My money is the only thing they care about, so it's what they won't get. Simple as that.
Zerospinboson, move on to better pastures is exactly what I did. There certainly are good enough alternatives out there.