The "new testament" "proves" chrstianity just as the "holy qur'an" "proves" islam and the "book of mormon" "proves" mormonism.
You'd recognize the fallacy in someone else's argument, yet you continually use it yourselves!
Have you ever researched all of the prophecies that Jesus fulfilled from the Old Testament? Born of a virgin in Bethlehem, etc? Go ahead. Take a peak. It won’t hurt just to look.