If you opened a case against the seller, then unless you selected the option saying "I Changed My Mind" or "Item Doesn't Fit", the seller would have to issue you with an eBay Returns Label via the case so that you could return the item for a refund. Such a label would have a tracking number on it, and once it had entered the postal system eBay would be able to put a trace on the item to see whether or not it had been returned to the seller. So long as the tracking shows attempted or successful delivery of the item back to the seller then you ought to be able to secure a refund. If the seller doesn't voluntarily refund your money after you have returned the item using the eBay Returns Label then once the option to escalate the case to eBay appears click on that option and ask eBay to step in and make a decision upon the matter. In the vast majority of cases eBay usually find in the buyer's favour, so you ought to end up receiving a total refund.
In the event that you selected either "I Changed My Mind" or "Item Doesn't Fit" as the reason for opening the case then you would have to pay to return the item to the seller. If this applies to you then send the item back using a fully tracked postal service, making sure that you upload the tracking number to the case details so that eBay can put a trace on the package and ascertain whether an attempt has been made to deliver the item back to the seller, or whether delivery of the item back to the seller has been successful. You should then be able to get your money back from the seller, even if you have to ask eBay to step in and resolve the matter on your behalf.
With regards to the abusive messages that you have received from the seller, I would encourage you to report the seller to eBay as suggested by @moldosgifts so as to bring the matter to their attention. However, if the seller persists in sending abusive messages then I would suggest that you also add his or her User ID to your Blocked Bidders List, ensuring that the Don't Allow Blocked Buyers To Contact Me option is also activated. Given that you've recently been in a transaction with this seller the blocks will not kick in immediately as they would have done had you never entered into a transaction with him or her, but after a period of forty-eight hours from the point at which you blocked the seller the blocks ought to kick in, thus preventing the seller from succesfully harassing you with any further unpleasant messages.
