Hello, is the train ticket office at Beijing Capital Airport currently in service?

December Last year 2015 it seemed out of service.
Is it true that foreigners can not buy tickets there but only at the railway stations? Because till March 2015 it was still possible.
When I buy or pick reserved tickets for travel companions, is it sufficient to hring there passport and the reservation numbers or do have the travel companions have to personally identify at the ticket office?

Thank you very much.
Meck from Germany