Unfortunately you're way out of time to open an eBay case, as you only get thirty days from the estimated date of delivery to do so. If you paid via credit or debit card you would have had to do a chargeback within one hundred and twenty days of making payment, so that option's gone as well.
In light of the above the only possible option you may have - although you may well be getting very close to the cut-off point, if it hasn't passed already - would be to open a case via PayPal if that was how you paid for the item. PayPal offer buyers a total of one hundred and eighty days during which to open a case, so if it's been less than one hundred and eighty days since you paid for the item, then if you paid for it via PayPal log into your PayPal account and open a case against the seller immediately. Don't forget to escalate the case within PayPal's twenty day cut-off period, otherwise the case will automatically time out on you and you won't be able to reopen the case.
If you've left it longer than one hundred and eighty days since you purchased the item then you're right out of luck with regards to being able to get your money back, in which case you'll just have to put this one down to experience.
Should you ever find yourself in a similar situation in the future ignore the seller's claims that they've posted the item and open an eBay case before the cut-off date, making sure that you escalate the case at the first chance you get if the seller continues to behave in an unhelpful manner. That way you'll more than likely get your money refunded in full, rather than ending up in a situation where you can't get your money back as a result of having fallen for the seller's delaying tactics so that he/she could run you out of time to open a case against him/her.
