All of the things you tried so far are good things to try so I will give some others. You can try an appetite stimulant for 3-4 days then try to feed again. Or you can try some chicken broth on the mouse/rat to change the scent. I had a stubburn Bumblebee that got to 600 grams and fasted for 2 months the stimulant worked for her. Assist feed is usually a last resort so I try not to use it if I can help it.