hello! I can't track this tracking number:RC928654458CN on China air post mail and it has passed 12 days since the seller shipped it to me.Could you help me?

Hi, Corina.
I cannot track any information about it. I suggest you to wait for a while and then try to check it again. Or confirm with the seller about the order number and then check it again.
This kind of situation is strange. Usually, the information can be tracked after you sent your parcel out one week later.