Don’t send a second package out if the customer simply wants a refund. Before submitting the evidence always try to work it out with the customer. Tell them that they have opened up a chargeback case and that if they simply wanted a refund, tell them that they should close the case first and return the original item (perhaps it was signed and received by a family member or friend).
Tell them that closing the case and returning the item (if received) would speed up the return process for them rather than going directly to the bank which can take up to several weeks or months.