Ive had a look at the transaction concerned and the history of the buyer. He has bought from one of my colleagues in the past so I checked out their history also. Firstly I understand this guy is away from the computer for long periods of time. If I look at his history of feedback left for others I can see its very intermittent and sometimes a month in arrears. (Even though most of his history is over 3 months old I can tell from an ebay item# approx when the auction concerned ended.)

Its possible he doesnt actually go in and check his paypal account. People that make their paypal payments by card etc. and never have a paypal balance often have no reason to do so. Ive had customers that didnt realise Id sent a refund or part refund etc. until months later.

If you havnt already done so, send one clear email to him requesting he checks his paypal account to understand he has had both payments back. cc the email to paypal, to the same address the email came from telling you one payment had been stopped. Do a 'request read receipt' on the email as well as marking it urgent. Doesnt always help but it may. While, as I pointed out before, it still may be some time before he gets the message, he left 3 feedbacks 24 hours ago which is an indication he is near to his computer at this time.
As an added 'extra', go to the ebay item and 'contact the buyer' which will generate a message from ebay to him. Copy and paste the text from the email and send it to him that way also.