Someone like WLC would say that objective moral values exist even if we do not know what they are (moral ontology versus moral epistemology), but, maybe god exists but is a perfectly evil Being:
https://en.wikipedia.org/wiki/Evil_God_Challenge
Can you disprove the existence of such a Being?
https://en.wikipedia.org/wiki/Evil_God_Challenge
Can you disprove the existence of such a Being?