iPhone 6 changing carrier, none work

I have an iPhone 6, A1586, which I purchased and did a screen swap to flip for resell. Initially, the carrier was listed as Sprint in the General > About section. I tested it with an active Sprint sim card….and it didn’t work. When I later checked it, it said T-Mobile, which I again tested with an active sim card, and again, it didn’t work. Oddly enough, the model is sold as a sprint device, so I don’t fully understand what is going on. I have attached two images that show it changing carrier.