'Call' in the Bible

Now if you call yourself a Jew, and rest in the law, boast in God,

As He also says in Hosea:I will call Not My People, My People,and she who is Unloved, Beloved.

for there is no distinction between Jew and Greek, since the same Lord of all is rich to all who call on Him.

But how can they call on Him they have not believed in? And how can they believe without hearing about Him? And how can they hear without a preacher?