There is nothing that eBay or PP can do; they have no idea if you have sent the item, and you have no proof of sending it.  PP offers seller protection to sellers who satisfy certain criteria = send by online trackable option.  

Police or ombudsman will also be unable to help you. Whether the buyer received it or not is not really the point, the point is that the CC holder is claiming they did not authorised the payment, it may very well be that your buyer has received the item but as they used stolen CC to pay for it the money has been taken back.  Or if their account has been compromised ALL payments would have been taken back, and it is up to the CC holder to go through the statements and weed out which payments are unauthorised.  Just because the buyer hung up on you means nothing; if they use the CC for many purchases they may have many people calling them and abusing them, and they just do not want to deal with each upset seller over the phone.