Why a United States passport holder denied 24 hours Visa free transit entry in Beijing?

Who is the appropriate authority, I can file a complaint about Chinese immigration designated desk?
We are United States passport holders having a 21 hour overnight transit in Beijing. The Air China booked a double room hotel and transportation in Beijing as per rule & regulations but Immigration counter girls refused us without even talking to us!
We were travelling From JFK New York to Pakistan via Beijing. We arrived there around 6.30 pm and our Connecting flight was next day at 3.30 pm after 21 hours. It was our worst nightmare sitting in transit area the whole time night and rest of day.
We contacted Air China multiple times with no help.