If an item is unsatisfactory in any way, contact the seller first. If you have no response in a week, raise a dispute giving the reasons. Tell the seller what you're doing. If you bought and paid with PayPal for an item through eBay, then it's through eBay you raise the dispute.
If one paid for an item directly to PayPal from an online shop, then you would still contact the seller as before, but raise the dispute directly with PayPal, because eBay was not involved with the transaction.
As stated before, keep copies af all the emails in case eBay wants to check them. If you sent them through the eBay service then they should be able to check directly because by the very fact you have raised a dispute implies that you want them to see any evidence.
Also, bear in mind the time factor. I have had occasion to use both dispute systems and they worked, even getting some unwarranted negative feedback changed. Good luck with this.