I called merchandise guest services, I believe the number is 1-877-560-6477, if they wont help you, take it back with you, I see you go in a month. We had an issue with a hat, noticed it almost right when we got home, DH shrugged it off, he actually was able to exchange it this past trip. We have found the merch services to be fairly reasonable, we just never usually say the exact date we just use the phrasing "on our most recent visit"
The biggest problem we have had recently when looking for specific merchandise the cast member kept telling us to look on the Disney Parks Shop app, and walking away. Being from Canada we can't get the app, never did find my star wars tee in my size...grrr