Your immediate response will be to scream at the producer that stole your work, but you should avoid publicly commenting until you have gone through the steps I'm outlining. You cannot fight every battle. I have instances where people steal my DJ mixes and don’t credit me. I work for a website that curates content that people steal and repost music from. And in the grand scheme of things, it’s pointless to spend time tracking down everybody that’s ever tried to use my work as theirs. But in the case of a artist profiting off of your work without permission, you have every right to reach out to them so you are compensated. Keep in mind though that if they made little money off of the record, you will get little, if any, money back.