Cruise Carrier denying boarding without Full Visa

I am boarding a Princess Cruise ship in Singapore in March 2018. The cruise terminates at Shanghai Cruise terminal and I then transfer to a hotel in Shanghai. 48hrs later I transfer to Pu Dong Airport to board a direct flight to London. I believe this itinerary falls well within the requirements to transit China in compliance with the 144 hrs free transit Exemption Policy but the cruise company will not allow me to board in Singapore unless I have a full Chinese entry visa. What is the answer?