It's not a fact. You cannot prove that the big bang theory is factual. You can bring up whatever evidence YOU think supports that theory. But the end result is still that it's just a theory. Again, it doesn't matter. The "evidence" you are referring to is still extremely limited compared to the age and vastness of the universe my friend. I really think you are giving humans a bit too much credit here. Everything we know is solely based off of our own perception of things, and our biasness. We are extremely restricted due to our current technology. Don't get me wrong, I'm not saying we aren't advanced. We've come a long way within just 100 years. There is so much more we could know if we were another 100+ years down the road. But even then, I still think we'd only be a TINY TINY TINY fraction closer to understanding exactly what happened.
Good example: Steven Hawkins' theory on how black holes operated held for 30+ years, until he disproved HIMSELF, totally revising his entire theory. And actually he ended up coming up with a theory that was the complete opposite of something he supported for 30+ years. We're talking about one of the most intelligent people on earth, and even his own iron-clad beliefs were proven to be wrong, assuming our perception of how the universe operates is correct.
So all in all, I'm not saying the big bang theory is wrong, and I'm not saying it's right. I'm not saying anything is wrong or right. I am saying we don't know, and believing in something you cannot prove to be right (religion included), well you'd have to be an idiot to believe that.