If you paid through Paypal from your credit card account, you can turn over the card and call the 1-800 customer service number.
Have all the dates, values and transaction numbers handy for the clerk to process your chargeback.
After you have your money back, leave appropriate feedback. You have up to 60 days for this. The most efficient feedback is calm and factual. Do not mention Disputes, as this can mean the FB will be pulled.
At the same time you will be asked for Detailed Seller Ratings. These are actually more important than feedback to the seller. The normal transaction should get Five Stars. The lowest rating is ONE star. No stars is a free pass.
When a seller's DSRs drop below 4.3, his ability to list and sell on eBay are restricted.