If you bought a money order from USPS, there would be no proof in your bank statement that you bought money order. The bank statement shows the amount you withdraw from your statement but it does not show what you did with that money. The only possibility I see here about getting a refund is if you paid for the money order at the USPS with your debit card. In that case, even if you don't have receipt from usps, they might be able to look that up for you and, probably, refund you if that money order has not been cashed. Therefore, just go to the usps and tell them your situation. I think you will get your money back .