Question about copyrights?

Okay so I bought a blu-ray combo pack and was tired so I wasn't paying attention and grabbed on that had been opened already and was missing both blu-rays that were supposed to be in there. When I took it back, they didn't have the same item to exchange for and I didn't want another movie so I asked for a refund. I was told that they couldn't give me a refund because it would be copyright infringement. I am wary of that excuse because how would giving me a refund for missing discs violate copyright laws? Is this really considered a copyright violation to give a refund when there are discs missing and if it is, I need it explained which they refused to do which also makes me suspicious. Thanks!