I am also understanding that Ren views Darth Vader as the true personality of his grandfather and that reedeemed Anakin was just a corrupted version of him. So even if a force ghost talked to him he might dismiss it as not his true character or some sort of Jedi trickery.
This might be true. What we’ve seen of Kylo Ren (especially after he killed his father) is that this kid has some issues. Who knows what’s going through this man’s head.
This is another good point…in assuming a rational villain, the possibility that Ren might be suffering from schizophrenia or psychosis was overlooked…it would not only explain his outbursts and patricide, but equally his inconsistencies in usage of the force…