Your reply is illogical and contradictory:
If, as you admit, that "our universe (space-time ) began with the big bang", then there cannot have been a 'before' the BB, as 'before' necessitates Time for that to have been a reality. But the real reason Space-Time did not exist is because they are conceptual, and arise only with man's rational mind. This is what most do not understand: that there is actually no Space-Time, even today. Once these conceptual overlays are removed (along with Causation), we are then able to see The Universe as it actually is, as The Beginingless Absolute that it actually is, outside of Time, Space, and Causation, as Vivekenanda tells us:
"The Universe is [none other than] The Absolute, as seen through the glass of Time, Space, and Causation"