china
Money will only be refunded by chargeback if it has been paid into the PayPal account. It is not your money, it is the buyers money and will not affect you whatsoever. People cannot claim back what they haven't paid, and they cannot claim back your money.
It will not leave your account in the minus at all, so stop worrying about that.
I would say it definitely was the internet cafe - the computer stored your details, so when someone tried to log in, it would do it automatically. Or you failed to log out properly.
Now, you have done everything you can do. Nothing bad is going to happen to you because of this, you will not lose money at all.
The only inconvenience is that caused by the need to cancel your cards, and that will be righted in the next few days.
You will always find somebody to advise you here:
http://forums.ebay.co.uk/forum.jspa?forumID=7
So, you can and shoud stop worrying about it now, and enjoy the rest of your weekend.