The irony is, many within Judaism believe they are Gods' chosen people, no matter what they do and this outright heresy has been adopted by Calvanists.
Again, you don't understand Calvinism. The Jews believed they were saved because of all the promises in the OT directed at Abraham and his seed.
Gen_26:4 And I will make your descendants multiply as the stars of heaven; I will give to your descendants all these lands; and in your seed all the nations of the earth shall be blessed;
Gen_12:3 I will bless those who bless you, And I will curse him who curses you; And in you all the families of the earth shall be blessed."
They claim that they (Jews) are the seed of Abraham and thus inherit all the promises. There does not seem to be any conditions in these promises.
Calvinists understand these promises as spiritual.
Rom_2:28 For he is not a Jew who is one outwardly, nor is circumcision that which is outward in the flesh;
29 but he is a Jew who is one inwardly; and circumcision is that of the heart, in the Spirit, not in the letter; whose praise is not from men but from God.
Gal_3:29 And if you are Christ's, then you are Abraham's seed, and heirs according to the promise.
We know election is not based on nationality, but simply God's choosing whosoever He will.
Rom_9:16 So then it is not of him who wills, nor of him who runs, but of God who shows mercy.
So a Christian can simply assume he is one of the elect because we are in Christ by faith, not because of who my ancestors were.
By the way, it is Romans 2:28 that gives us the idea that all those Jews who were saved in the OT had that circumcision of the heart.