Using my story without my permission?

in 2009 I wrote a story that was subsequently published in an anthology . after my contract expired a friend of mine wanted to do an audio play of the story. after multiple recording sessions we can't get his voice to match what I want for the character . he refused to look for someone else's voice and I pulled my permission for the project . he says he's put too much effort into it and it's going through no matter what . we have not drawn up a contract and I have not expressed my written permission . how do I protect my story from being stolen in this manner ?