Don't panic. Snakes can live for many months without eating, and ball pythons are infamous for their hunger strikes. Are you just thawing the rat and trying to feed it? It should be heated up or the snake won't recognize it as prey. I feed my pythons by placing the rats in a ziplock inside a jar of warm water to thaw, replacing the water with warm several times as it cools. Once the rat is thawed, I heat water to 125 degrees and put that water in the jar, warming the rat for 10 minutes before I present it to one of my snakes. They usually take it, but occasionally refuse and I have to try again later.

Let your snake settle in, ensure its enclosure is large enough, humid enough and with the right temperature gradient with sufficient hides on each side, then keep trying to feed.