Well a quick check of that URL shows an HTTP 404 error. I would suggest continuing to ask for help from Kobo, as they are the only ones that can fix it so you can download that book. (It's a misconfiguration on their server).
ps If you are having problems with contacting Kobo, you may want to ask in the
Kobo forums to see if anybody there has better ideas for getting hold of them. I've not heard of them being generally unresponsive.
pps Welcome to MobileRead.