Someone once asked...
Someone answered with kindness...
After that long you may just have to accept that forgiveness might not ever come from this person, and that perhaps you instead need to focus on finding a way to forgive yourself. We all make mistakes, that's what makes us human. It sounds like you've tried your best to make it up to whoever it hurt, so at this point, does punishing yourself for it actually change anything? Give yourself the grace to move on, and remember, this is just another human. Maybe one of their mistakes is not forgiving you?