AmEx doesn't allow DCC,, so it's a good alternative for China and other countries were this scam is prevalent.
If you have a document showing that you did not choose to be billed in your home currency (like the receipt without the box ticked), you can dispute the charge with your credit card company. The Visa/MC terms explicitly require to be given a choice. If you weren't offered a choice or they ignored the choice you made, your claim should be confirmed.