The Big Bang Theory is the only one of several possible theories on the origin of the Universe.
However, it is the only one which, so far, has consistently explained the observed phenomena (eg background microwave radiation). All the others have failed in this in explaining at least one such.
This is not to say that it is the final word - there needs to be just ONE observation that cannot be explained by the theory for it to fall flat.
So, for the time being, the Big Bang Theory is good.
As for religion, my own says that the creaton came about almost instantaneously from "OM". This concept is quite consistent with the theory.
And my final belief is that though the pundits are hard at work getting closer and closer to t=0, they wil never actually be able to reach reach it - God Bless them - as then they would know the mind of God (Dr Hawking's words paraphrased).