Most credible theories explain very well what might have been before the "Big Bang". One is that we're part of an infinite number of universes, and when 2 of them touch, another is created in a "Big Bang". There are others.
Let's face it. We barely understand 5% of the universe (visible energy and regular matter). Fully 95% of it is something we don't even know how to detect yet.
We've not been able to measure it with modern instruments, yet some guys 2000-3500 years ago figured out where it all came from? Me thinks not.