If you’ve sold them your voice under the condition they can do whatever they like with it, I don’t see it being unethical. You walked into it informed (presumably) and accepted the “pennies” (presumably). It may be stupid. What comes out may be shit. But it’s not “unethical”.

If they stole your voice, or if you had content limits that they breached, or if they’re paying you less than you agreed for, then yes, it’s unethical.