I would assume that PayPal uses an ACH (Automated Clearing House) transaction. I do not know thier overall policy but ACH transactions can be reversed. I would contact PayPal and see if they are willing to reverse the transaction and the I would also contact your bank. I would tell your bank that the debit to your account was not authorized and ask them to return the debit. That will probably get you in some hot water with PayPal but it may help them to resolve the problem also. ACH transactions are bank to bank transactions where PayPal initiates a file that containes both the debit and credit to each bank account. The funds are not verified as good funds in the senders account unlike a Fed wire transaction.
Hope this helps.
Hope this helps.