Your first option is to let the seller know about your problem (via eBay message), as they might be able to help. Communication is key here, so don't ambush the seller in this scenario and give them the benefit of the doubt.
Otherwise, if the seller doesn't respond back or make any effort to fix the issue, then --
Open a return request to return your item for a full refund (go to your eBay purchase-history page, then select 'return this item'). Hope this helps.
