I am an adult and my father passed away in October of this year and I was told that I couldn't receive the remainder of his benefits because I was over 18. When I was younger I had surgery and received disability until my mom got married. My father has been disabled for several years and I never received a disability check from his disability check, how would I go about trying get his disability.

Are you talking about SSD? A private policy? Something else?

You are not entitled to benefits after he dies if you were not entitled to benefits while he was alive.