YOU are the buyer, so don't understand "the buyer opened a case".
You opened an item not as described case. You received a prepaid return label and returned it.
It's doubtful that eBay is "working on the case".
You need to contact eBay through Facebook or Twitter and state that you, the buyer, opened a case, received a return label and returned the camera. Presumably the seller has received it. If he does not refund within 4 days of receiving the return, ask eBay to get involved.