People have to want to come to an understanding of the truth. That applies to any truth.
There is none so blind as one who will not see.
You are wasting your time and energy attempting to open the eyes of those who are resolutely resistant to facts. Save your time and talents for more productive endeavors.
Sad indeed. But you have evidently tried for a long time. You are not ultimately accountable for the steadfast refusal of others to cultivate an open mind.
I would also suggest that perhaps you now decline to enter into further discussions with him predicated on the same basis. I would say something like: “I’m not going to continue debating this with you, because you think you already have the answers and aren’t open to facts and data that show you’re wrong.” Withdrawing from unproductive arguments sometimes makes people reconsider.
I’ve found that those who steadfastly cling to a position and remain impervious to new information are in fact: 1) seeking to bolster their own psychological insecurities; and 2) craving the attention of others. Remove this crutch and they start to crumble.
Good luck and Godspeed, fren.