Switching itself off after housing replaced

Since replacing the full rear housing on my iPhone x with one from eBay my phone re starts about every 2-3 minutes and face id is not available any more. Everything went back as it should but I can’t stop it from restarting all the time. I’ve done factory resets and software updates through iTunes and only when I'm safe mode does it stay on long enough. Any help would be much appreciated. Thanks.