Heck, the guy could have used osC to take the payment and then Moodle to administer the exam. Once payment is accepted, it could shoot off a password which would forward you over to the moodle part of the site where the user has access to the exam. Doesn't sound that bad to me.
However, to give the guy a break, osC is absolutely a big mess, especially if you're not familiar with the way it's set up. There could be a big learning curve there... as well, I know you're a paying customer and I'm all about the importance of customer service in an extremely competitive market... but maybe he has taken on more projects from other customers and isn't the best at project management and multi-tasking. When we estimate projects, we give a reasonable time frame for completion based on our current work load... i.e., something could take 10 hours to complete, but that doesn't mean it will be done in 10 hours from now. We have numerous other projects going on and a limited amount of hours in the day, so we have to juggle things from time to time. And we all know that nine women cannot make a baby in one month. Some things just take time.
6 months is a long time however for even a 20-40 hour project, imho. I agree with the others - you should confront him, and if it can't come to a resolution there are numerous other budding web developers out there who are hungry for work.