REPAIRSUNIVERSE.com Sent me the wrong item, now they don't want to exchange. BUT even worse... Las Vegas Nevada

I ordered a screen for an iPhone 7plus but they sent me a screen for an iPhone 6plus. When I spoke with their customer service they said to sent the screen back so I did. Several days later, not hearing anything back from them, I called in and was told that they weren't going to send me a replacement cause the screen was damaged. Please get this clear. The wrong phone screen they sent me was damaged so now they won't exchange my screen for the one I ordered. What can I do? It's me against their cunstomer service. I had bought 3 other screens from them with no problem at all an I enjoyed helping a small website other than Amazon and other billion dollar companies but now I feel like I have learned my lesson. I paid $80 for it now I don't have anything, they kept the screen and haven't contacted me at all. I'm lost. Please help.