As has already been mentioned, it would help if you had explained the matter in a bit more detail, as the more detail you provide the easier it is for people replying to your post to give you more accurate advice.
eBay allow buyers up to thirty days from the estimated date of delivery to open a case if need be. If you haven't run out of time by the time you read this reply go back to your Purchase History page, locate the item in question and look for the More Actions option on the right. Click on that option and when the drop-down menu appears select the option to return the item. The reason for wanting to return the item to the seller will be Item Not As Described.
After opening the case wait for the seller to respond. If he/she responds and issues you with an eBay returns label then print off the label and affix it to the package that you use to return the item to the seller.
Once the item has been posted back to the seller then as soon as eBay see that the item has been received by the seller, or that delivery has been attempted, your money will be refuded. If, on the other hand, the seller proves to be obstructive and will not help you in any way whatsoever, make sure that you escalate the case to eBay as soon as you get the chance to do so. eBay will then step in and force the refund, regardless of whether or not the seller agees with the decision to do so.
In the event that you are out of time to open an eBay case then you will have to go about chasing the seller for a refund via a different means. If you paid for the item with PayPal then log into your PayPal account and open a case against the seller there. Unlike eBay, who only offer buyers thirty days to open a case, PayPal offer buyers a total of one-hundred and eighty days during which to open a case, so if you are still within this timeframe open a case against the seller that way. You must ensure that you escalate the case before PayPal's twenty day cut-off point if the seller becomes obstructive, otherwise the case will automatically time out. If you escalate the case in time then you ought to receive a total refund.
If you're out of time to open an eBay case and you paid for the item using a credit or debit card rather than using PayPal then you could still get your money back so long as you purchased the item less than one hundred and twenty days ago. If this is how you paid for the item and you are still within the time limit then if you opt for doing a chargeback you could end up with your money being refunded.
As you can see, there are three different options here for you to use in order to chase the seller for a refund. If you just throw in the towel and say "I'm never buying on eBay again" then you can kiss your money goodbye, but if you chase the seller relentlessly for a refund via one of the methods suggested then you could end up with a full refund of the money that you paid the seller for the item.
