What is the Christian’s new name?

Answer:

The phrase "new name" is only stated three times in the Bible:

"The Gentiles shall see your righteousness, And all kings your glory. You shall be called by a new name, Which the mouth of the LORD will name" (Isaiah 62:2).

This is talking about the Messiah being called by a new name.

"He who has an ear, let him hear what the Spirit says to the churches. To him who overcomes I will give some of the hidden manna to eat. And I will give him a white stone, and on the stone a new name written which no one knows except him who receives it" (Revelation 2:17).

This is clearer in the Greek than in the English, but the new name is the name of the giver and not the receiver, that is Jesus' new name. It is explained in detail in "Does Revelation 2:17 mean we will have a new name in heaven?"

"He who overcomes, I will make him a pillar in the temple of My God, and he shall go out no more. And I will write on him the name of My God and the name of the city of My God, the New Jerusalem, which comes down out of heaven from My God. And I will write on him My new name" (Revelation 3:12).

This is basically the same as Revelation 2:17. The new name is that of Jesus Christ.

There is no passage saying that people are given a new name when they become Christians.