When the seller cancelled your item did he refund you or has he kept your money? Check your PayPal account - if he hasn't refunded the money then open an Item Not Received case in eBay and escalate the case for eBay to make a decision on eight days later if the matter still hasn't been resolved satisfactorily. You should receive a full refund as eBay nearly always decide an Item Not Received case in the buyer's favour.
If it turns out that the seller has been banned from selling on eBay and you still haven't received a refund then open a case via PayPal if that is how you paid for the item. You should be able to get your money back that way if the seller has been banned from selling on eBay and you haven't got your money back yet.
PS: In order to open an eBay case click on Help & Contact and you should see a row of pictures of your recent purchases. Click on the item in question and you should be able to open an eBay case that way.
