Wow, that really sucks a lot. Such a shame, the illustrations are great. It is so tricky to communicate reasonable expectations, selling your stuff, getting a decent pay for your effort and handle some ass-hole customers out there. I have a similar story where I made this picture for a customer (who had paid me in a different job). When I refused to send him the originals he refused to send any money. I used the Swedish law and sued him, but then it turned out he was a bluffer using false identity. So my tip for everyone doing illustrations for commission - check people if possible and don't send originals before you get paid. Hope this post give you something back!