They made the mistake, and if it can't be corrected without money coming out of my pocket, then I wouldn't make much of an effort to return it.
A few years ago, I ordered something from an online store on Cyber Monday. The company's website had great sale items and couldn't up with the traffic, so the website kept crashing through out the day, but I managed to place an order for three items before it crashed for good.
My stuff arrived, I was super excited, but noticed that the charge never hit my credit card. I watched for two weeks before calling. The first time, I was on hold for nearly an hour and finally got a hold of someone only to get disconnected, from their end. Two days later I tried again, got a hold of them and when the lady tried pulling up the info, their system crashed. I didn't try again after that. I felt bad about it but I couldn't get a hold of anyone to fix the error and had a life to live, and I was not able to spend hours on hold.