If the estimated delivery date has passed open a "not recieved dispute in the resolution centre. When it's been open for 8 full days, timed to the minute you will see the option to ask ebay to step in. When you do your refund should follow and the seller will get a defect on his account.
If by chance you are too late to open a case in ebay ( 30 days ) you will still be able to open one in paypal. Paypal cases need to be escalated within 20 days.
