Hi,
Craftsmen can pretty much get away with anything these days, but this is really extraordinary.
If he doesn’t want to separate labor and materials, you probably won’t be able to force him to do so unless there is some tax regulation that requires it. Keyword: "undeclared work".
You can turn his whining about the material list around. Inform him in writing (!!!!) that if there is no previously agreed material list, you reserve the right to refuse acceptance and payment for the materials he installed and that he is then obligated to procure and install any stuff you request.
Then the toilet including labor can be the 24 karat gold version. After all, that’s what you chose and it will surely be on his list, which he refuses to show you….
And he has to confirm this agreement in writing, otherwise he is not allowed to enter your construction site. (I hope you are the builder and didn’t buy from a developer. If the latter, you’re really out of luck).
Realistically, it will come down to you having to reassign the contract. It seems no cooperation is possible with this guy.
Best regards,
Andreas