Yesterday I called the Shanghai's travel company that was related to last month's travel and I talked about the incident (I had been cheated in a "Cafe").
The Chinese travel agent spoke Japanese very fluently and said you should have notified the police of the incident immediately after that.
As you were in Shanghai there ought to have been the policemen who can understand Japanese language. I've heard that some Japanese were cheated into paying more money(about 250,000yen).That was what the Shanghai's travel agent said.