How do we know we made him up? Because he goes down everybodies chimney in 24 hours and this is obviously impossible, therefore the santa that we describe today CANNOT BE real. So, he's made up.
You are currently experiencing a lucky and very brief window of awareness, sandwiched in between two periods of timeless and utter nothingness. So why not make the most of it, and stop wasting your life away trying to convince other people that there is something else? The reality is obvious.