Sorry. At this point I have no idea, especially if you have removed the plugin and folders, and you said there wasn't anything in the database from us. Caching and mail queues were the only things I could think of. As the plugin is off your site and we have refunded your money for stated reasons, there doesn't seem to be anything left for us to do.
Good luck in your future endeavours. I wish I had something else to give you.
tim
