Who was going to refund you?
If it was Paypal, look in your PP account and also in your credit card account.
If you pay from your card through PP (the safest way) the refund goes there. Otherwise it should be in your PP accounting.
If it was the seller and neither account shows the refund, have you started a Dispute?
If you have, and the seller has not refunded, escalate the dispute to a Claim. Then PP will refund you and go after the seller for their money.
If you have not started a Dispute, do so. The Resolution Centre is at the bottom of this page.
The first step is to contact the seller, but you have already done that, so go on to the dispute and claim.
Was this a Mutual Cancellation? The seller should have refunded you before you accepted the cancellation. Call eBay.