Well it sounds like you have been feeding your snake mice? So moving over to rats is not going to be easy, the smell different and after a year the snake is looking at the rat like its not food doesnt smell the smame or look the same, so its not going to be easy to change them back over to rats but dont give up. KEEP TRYING. try to take a mouse and rub it over the rat so the rat will smell like the mice. BEST of luck