USA citizen - only got a 20 day L visa

Hi, I'm an American currently visiting Vietnam and got my Chinese visa in Hanoi. They knew we needed to stay for 30 days, but only the travel agency only gave us a 20 day one. They say Vietnam can only get 20 days from China and we can "easily" get an extension while in china - 15 more days for free. What?! Is this true? Weve asked other travel agencies and they say it's not true, and the Chinese embassy is closed until tomorrow. Anyone have any idea what is going on?