Why aren't we given a chance in afterlife to redeem our wrongs?

This is about christian religion. What if a person did know about Jesus and the bible during his/her life on earth but didn't believe in them. He dies and is doomed to hell. But why can't the All-Merciful, All-Forgiving God give the person who realized after death that he was wrong, another chance to redeem themselves? Why do they have to go to hell for all eternity? that's not very fair.