I bought books during the April Fool's sale, but wasn't immediately credited with the promised micropay dollars. I emailed them right away. By the next day, my account had been credited and they emailed me to notify me.
I've also had great experiences (polite, helpful and prompt) contacting Ebookwise about my ebook reader when it was damaged.
Did you use the contact form on the site? If so and that's where the problem was, my only other suggestion is the official yahoo group:
http://groups.yahoo.com/group/Fictionwise/