They are trying to scam you. What does the tracking number say? If the buyer has opened an item not received dispute, make sure you enter the tracking number into the dispute. DO NOT ask ebay to step in and help via a dispute or they will automatically close it in the buyer's favour. You then lose the money and the camera.

As others have said, get onto ebay asap and explain what it going on. You might have to reinforce what is going on, because they aren't real bright. If you don't have much luck, ask to speak to a supervisor.