I sold a number of short stories to a publisher several years ago. There was no contract, just the one-time payment. These stories have been available for sale from their website ever since. But now I notice they have compiled a book of my stories and are selling it on Kindle. I feel that I'm entitled to royalty payments on this book. I didn't sign away my rights, in fact, I didn't sign anything at all. Could anyone tell me what my legal position is?