There is a certain amount of time that needs to lapse before ebay will step in to examine what went wrong. This allows the seller an opportunity to fix the problem for their buyer. How much time has passed since you opened your case?
Like mjwl2006 says you have to give the seller a bit of time. According to the Money Back Guarantee pages it is 3 BUSINESS days. That means Monday-Friday, not weekends. If that was what you were asking about you can see it here under the pre-set question
The seller didn’t resolve my issue—how do I ask eBay to step in and help?