You really aren't that smart if you actually think this is something real that could happen.

1) You knew any graphic files were available to the general public to upload and/or edit and still proceeded to upload 'payed work' to it, you knew the risks before doing this.

2) You are using GraalOnline and a free-service they provide to make money in the real world (by selling products to people who are also well aware of point #1) so if anything, they have the right to remove your content from Graal and they are in no way responsible for any third-party transactions you and your 'customers' have made because you made no attempt beforehand to discuss said transactions with them or discuss the possibility of them protecting your work you also made no attempt to ask if it was okay for you to use their service as a means to earn profit - instead you sold your 'work' knowing point #1 and tried to complain afterwords, any lawyer and judge would laugh at you (lets face it, we all know you haven't lawyered up).

3) If we are viewing this from an artist POV, your art isn't really worth stealing (which is why he edited it - to improve it) so you really shouldn't be worrying this much.