Chinese Embassy UK - London

Hi,
I called the Chinese Embassy to confirm if I needed to arrange a transit visa in advance or collect this at Shanghai airport. I'm travelling from Thailand on the 15th Nov and leave Shanghai to the UK on 18th (so within the 144 hours) however they said they had not heard of this before so could not advise.
Is this possible the embassy are unaware of this?
Do I need to make any arrangements before my trip or can I arrive at Shanghai and obtain this at the airport?

Thank you