It's China, so in this case (relatively advanced financial transaction), I would bet its a legitimate claim on their part. Keep the email just in case for potential dispute purposes. Then I would say, call them and tell them to cancel the booking.

You can make bookings on the ground in China (at the airport where some English will be spoken) or at the hotel where you stay (for a nominal fee but similar price) or if worse comes to worse, on the phone with ctrip where a delivery dude will come and deliver your ticket by hand.

FYI, paying in cash at their office sucks. It's in some small building in XiCheng District right on XiZhiMen and was very tough to find.