It's a frustrating game of whack-a-mole with these assholes.

Good to hear you were successful at getting them taken down (this time). At least you know the drill now and hopefully will be just as effective next time it happens.

Comes with the territory of being an adult content producer, sad to say.

NOTHING is considered 'public domain' unless it's explicitly stated as such - content must be labeled (by the original owner) as either "royalty-free" or "public domain". Without that signed statement, the material is copyrighted and subject to all copyright laws and penalties for infringement.

And as someone already said above - it's also subject to 2257 requirements. The pirate is fucked if asked to produce 2257 to prove all models were legal age and participating consentually.