Do I need a visa for layovers in China?

We fly from SFO through Wuhan and Guangzhou to our final destination in Thailand. On the return, we will again stop in Guangzhou and Wuhan before continuing on to SFO. Outbound, we stop for 2 hours and 13 hours, returning we stop for 5 hours then 2 hours. A China Southern Rep told us we need a visa because we make 2 stops twice. Is this true? Everything I read on the travel sites say we don't.