If travel agent cheats on travel itinerary, who do I contact to lodge formal complaint in Shanghai?

Yeoh, you should contact local tourism bureau to lodge your complaint. The phone number is 0086-21-64393615. However, I am afraid that they may not be able to communicate with you in English very well.

If possible, you may find your Chinese friend to help you. If you don't have a friend, you should visit the bureau in person.
Address: 10th floor of Shizheng Mansion, no. 100 on Dagu Road.