Sold me the wrong product and can't get a refund

I went to location and asked the representative to find a shield for the phone I purchased through Xfinity. The person ended up selling me the wrong thing. This location is high traffic and hard to find parking so I went to another location to return the shield. The rep there said the system would not allow him to do the refund and I had to go back to the original location. That's not an option. How do I get the refund?

Thanks