144 hours transit visa to China (Mongolia-China-Denmark)

My travel partner and I wish to travel from Mongolia by train to China before returning home to Denmark, which is our homecountry. We have been told, that we can receive a 144 free transit visa at the railroad station in Beijing. We have received knew information about, that the Visa is NOT obtainable from Mongolia.

We will be leaving in a week, so its very important to now.
Thank you.