Night train from Beijing to Shanghai

I'm going to China in September. I'm going to be in Beijing some days and then I want to go to Shanghai. I'm looking for a night train, but Chinese tourist office in Spain says there are no night trains. I can’t find any night train at Travelchinaguide to buy, but there are listed on the schedule. Since July there are high speed trains between these cities, maybe night trains has been disappeared. So, I don't know what to do. Does any one could explain me this mess and where can I buy tickets for night trains?
Thanks