both of your statements cannot be true...at least at the same time.... even those who deny Him as a being, must admit that God exists at the very least as an idea....therefore it could be said that mankind invented God.
something created us....even those who believe the big bang created us...would then be placing Big Bang as god
There is a Zen Buddhist Koan like this question. A young monk one day goes up to a master and asks "If all things come from the source, and all things return to it, from where did the source come from, and to where will it go" to which the master replied ""When I was in Jing Zhao, I made a cloth shirt. It weighed seven pounds."......
For the God of the Christian religion, or Islamic one for that matter, one of the prime requirements is that he/she/it is omnipotent, omniscient and immortal, basically always has been and always is. If that were true then nothing created God, he's just always been. Of course different religions have different ideas and like giving their Gods a bit of a history, usually, in cases of Egypt and Greek myths, the universe is a big soup of chaos, out of which grows physical things, like Titans or gods and sometimes the world. Other times a god pops up, kills some chaos god, and then makes the universe and heavens out of its corpse...