Anything I've ever bought online that's maternity says I can only return it through the mail.
Well, I bought a few things before they changed their free return policy and I called customer service to see if I can still return for free. She said no, but I could return everything to the store. I told her it said return by mail only and she said most stores would take the merchandise back. Well, I tried it and it worked. So, maybe try returning it to the store 1st so you don't waste $6.
Re: Old Navy returns that say Return by Mail Only