From Barcelona

Hi,
We are two spanish citizens travelling from Barcelona to Beijing, we will arrive there on 8th june at 4:15am. The next day in the afternoon we are going to Pyongyang (North Korea). We are flying from Barcelona with Air China and they ask us a special visa for us to take the plane because they say that the the flights have to be in the same itinerary. Can you help us please? We don't know what to do, thank you.