Firstly try to contact the owner of the paypal via emai. If you wouldn't get any response , just file a chargeback.
Simply go to the resolution center, search for the transaction and file a charge back. thats all, you'll be done
Log in to your PayPal account. Click the History subtab. Click the Cancel button in the Action column of the transaction in question. Click Yes. Your Money Request or Invoice will have been successfully canceled.
First you should contact to owner of that paypal account.And tell him the story I think he/she will return your money.
Why open a dispute?! At first try to contact the accountholder of the account you sent the money to and tell him about the situation. Usually there is no problem and he will just refund it to you. If this doesn´t work then you can claim a dispute, but not before because it can last longer if PP has to "resolve" the dispute before, although the reciever would have just refunded if he had known about the fault