I come from a divorced family and had a hard relationship with my father with and without my mother’s opinion of the situation.
But, the kid needs to speak with his father. Those two need to go to counseling together. Yes, the kid is listening to his bio mother. This is what happens and I am sure this is just one part of the story. But I do agree that college is a privledge and expensive. Not seeing the kid for 3 years is not just on the 15 year old. There is more to the story.
I wouldn’t use the paying for college as a bribe but something has to give. Maybe the father would like to take his son on college visits to ones he can afford. This would be great use of bonding time. Talking about college and helping with the application etc.
It is important to repair the father /son relationship first. Then repairing to the rest of the family.
Texting daily with no response is just landing on deaf ears,if I am understanding. Has the father gone to teacher /child conferences at school? Has he gone to games kid has participated in?
Fix this first and the rest will follow.