If you have paid a Spanish ticket by transfer within the last 6 months, you might be in trouble. When paying by transfer it is always important to include the 'expediente' number in the transfer form. If you fail to do so, the fine will be unpaid for the Spanish authorities. Several drivers in France have found that the Spanish authorities are insisting that they must pay a fine they have already paid.
Our advice if you choose to pay by transfer is to call the Spanish authorities two weeks after making the transfer to confirm both that they have registered the payment and that the file has been closed for payment (which means you will receive no further communications, and the car rental company won't charge the fine amount plus a fee on your credit card).
I've found three similar cases in different forums on the Internet, so if you choose to pay by transfer make sure to confirm that they register your payment properly.
