Visa - Eligible to travel?

Hi! I travel with my girlfriend to Bali Island via Shanghai (Prague-Paris-Shanghai-Denpasar) and after two weeks return in the same way. Are we eligible by both trips to get free transit for visiting Shanghai city? Second question - Should I write or call to carrier before check-in or I can announce during check-in that I will use 144 hour free transit? From website it's not clear to me.

Thank you in advance for your answer. SC