24 Hour Transit Without Visa

I am flying to Bangkok Thailand with a layover in China.
My flights are as follows:

USA to Shanghai, PRC to Bangkok (the layover is 3 1/2 hours )

Coming home

Bangkok, Thailand to Chengdu, PRC (layover 6 hrs) to Shanghai, PRC (layover 1 1/2 hrs) to USA

I land in Chengdu at 1:15 a.m. on Friday May 6 and leave Shanghai for USA at 11:40 a.m. This is less than 24 hours.

Everything I have read says that I can use the 24 hour direct transit for both going and coming home. I need some verification that this is indeed true. I keep getting the run around when I actually talk to someone and I have called the Consulate General of the People's Republic of China in Chicago several times and always get the message that the mailbox is full. Please help as my trip is very soon.

Thank you,
Amy C