Legal Question in Entertainment Law in California

As you seem to be aware, extra is a separate category of work than production assistant and, customarily, when a person on a film set performs more than one function, they get paid for each function (although not necessarily a full salary for each). Especially where it is a convenience to a producer who finds himself "short" a person and needs to keep shooting. As a first step, you could contact the company that employed you (the one named on your paycheck) and point out you worked as an extra and expect to be paid for that. You should receive the same amount they paid the other extras. If unions were involved, you could report it to the actors' union.

You might also file a wage complaint with the California Labor Commission, who could help you get paid. They can also recover penalties for missed meals and overtime, if applicable.

If you didn't sign a release, then that's a problem for the employer. It means they didn't secure the right to use your image, which could be used as leverage in a lawsuit. But that's a little technical and you would need a lawyer's help to invoke a copyright claim. However, you could refuse to sign a release now until they've paid you what you're owed.

The above is general information only, should not be construed as legal advice, and may not apply in your case. No attorney-client relationship is formed by this posting.