There are three levels of Buyer Protection. Unfortunately you may have timed out on all of them, depending on what you mean by a few months,
The shortest deadline is eBay-- about 30 days I think. It used to be 45 days from purchase, but they changed that fairly recently.
The next is Paypal. They allow 180 days (six months) to complain.
Go to the PP site, find your payment and the transaction number.
Go to the Resolution Centre and choose Item Not As Described.
You need to give the date of return shipping and Proof of Delivery to the seller. Good thing you used tracking.
The Proof of Delivery should be enough to have PP demand the seller refund. If he doesn't, PP will refund you themselves and go after him for their money. He will not be happy with the fallout from that.
If PP can't help, usually because the buyer passed the deadline for opening a Dispute, you could go to the credit card you back your PP account with, phone the 1-800 number on the back of your card, and go for a Chargeback.
And in future, once the seller has the item back, he should be refunding within seconds, although it would be polite to allow a couple of days for him to get organized.
After 48 hours, start the Buyer Protections.
You also have 60 days to leave feedback and Detailed Seller Ratings.
And you can add a Response to any feedback you or the seller left indefinitely.
Remember that the most effective Responses and Feedback are calm and factual. "Did not give promised Refund on Proof of Delivery." for example.