Ask the seller if he refunded through Paypal.
If so, the refund would have gone to the correct address.
If you back your PP account with a credit card, the refund goes back to the credit card. If you used a PP balance it goes to your PP account.
If he refunded directly, without clicking on the refund button on the PP payment, he may have got your email address wrong.
If you have returned the item, and the seller is not being helpful you can go to the Resolution Centre at the bottom of this page and open an Item Not As Described dispute. PP will straighten it out fairly quickly. But you only have 45 days from purchase for this.
