www.usps.com states no refunds on MO unless damaged-
Money Orders are not eligible for a refund. However, if a money order is spoiled or damaged, you can request a replacement money order, write your name as the recipient, and then cash the money order. To replace a money order complete the following steps:
1.
Take both of the following to a local Post Office facility:
*
The original United States Postal Service money order.
*
The purchase receipt for the original money order.
2.
Fill out PS Form 6401 (Money Order Inquiry).
3.
The money order will be immediately reissued.