After Ctrip booked the ticket, Ctrip now told me that the airline flight was cancelled. What should I do?

Of course not! If the flight changes, there are generally two solutions: one is to contact the booking point for a full refund and re-book. Go to the airline counter and ask them to change to a suitable flight. As long as there is an agreement between airlines and there are vacancies, the airlines will help you change them (regardless of the outside price). In this case, it is of little use to find an airline ticket sales agency. They are only responsible for sales, and it is most direct and useful to find an airline.