"We've gone out and proven it, "
Really? Evidence please.
"So I ask you, how can you prove that God isn't real? "
I don't prove negatives. You are making the claim for the existence of god(s) so it is up to you to provide the evidence for such a being.
Not once in the history of the world has any evidence that would stand up to scrutiny ever been advanced for any god anywhere.
So, convince me.