One of the more difficult things to do in life is to preach to people whose heart is hardened and never intend to change.  This is not a new problem.  Consider what Jeremiah had to face.  Jeremiah 7:22-27 reads, "For I spake not unto your fathers, nor commanded them in the day that I brought them out of the land of Egypt, concerning burnt offerings or sacrifices:  But this thing commanded I them, saying, Obey my voice, and I will be your God, and ye shall be my people: and walk ye in all the ways that I have commanded you, that it may be well unto you.  But they hearkened not, nor inclined their ear, but walked in the counsels and in the imagination of their evil heart, and went backward, and not forward.

Since the day that your fathers came forth out of the land of Egypt unto this day I have even sent unto you all my servants the prophets, daily rising up early and sending them:  Yet they hearkened not unto me, nor inclined their ear, but hardened their neck: they did worse than their fathers.  Therefore thou shalt speak all these words unto them, but they will not hearken to thee: thou shalt also call unto them, but they will not answer thee." 

Before Jeremiah even warns the people, he is told that they will not listen.   Still, it did not aleviate his responsibility to preach to them.  We might think that if we already knew the outcome, why waste your time and energy preaching.  The same reason could be given to answer why God told Pharoah, "Let my people go" when He knew Pharoah's heart was hardened.   The preaching of the gospel will always produce two effects.  The difference is not in the truth of the gospel or some injustice of God that arbitrarily chooses whom He will save.  The difference is in the heart.  The parable of the sower illustrates this truth.  The same seed was scattered, but it fell on different kinds of soil.  It is like the heat of the sun that can both hardened a clay pot or melt a wax candle.   The same heat was applied to both but the two different results was based on the character of the objects under that same influence.  

So, do not quit because no one will listen.  Give all the opportunity to accept or reject but just know that the majority will not hearken.  It's no reflection on you.  As far as you are concerned, you just lay it before all to hear and once that is done, you have performed the will of God.  They get to choose life or death.