He can't 'get into' your account unless you sent him your credit card number. Which apparently you are pretty lax about. This a very public forum and you posted the number here.
Sigh.
If you paid through Paypal, the listing may have had "immediate payment required' and when you agreed to the sale, the money was immediately taken from your Paypal account from your credit card account.
No one can see your credit card information if you pay through Paypal.
If the seller has been paid, assume that the item you purchased and paid for has been sent.
You could try using "contact seller" on the listing and asking that he request a Mutual Cancellation which you will agree to when you have your refund. If he does, AGREE IMMEDIATELY. When the refund arrives, leave positive feedback.
If the item has already been sent, you can refuse the package or you can return it unopened to the seller. It is best if you are returning it to use a tracked shipping service. This can be expensive if the seller is overseas.
If the seller refuses the refund, you can go to your credit card, with proof that you have returned the shipment, and ask for a chargeback.
In closing, you are given two chances to back out of a transaction before you pay for it. And there is a short interval after purchase, during which either the buyer or the seller can cancel the sale unilaterally.
But you have to pay attention.
