There is one chance to find it out. If you allready have given your creditcard- or bankaccount number to PayPal. After a few phonecalls and sending a copy of your drivers licence or other documents, they will identify you while sending a few cents to your bankaccount. You have to identify yourself via another phonecall to tell them the correct amount they send to your bank (something like 1 to 20 cent), and the text submitted with this payment. But if you have only this $20 on your PayPal account, handling this may cost more than you earn.