Stay consistent. A lot of people change the methods they use every week, which just confuses the snake. Do the exact same thing every week. Eventually your snake will take it.
I had the same issue a while ago with mine.. Switched to live one week. Then back to ft. And he didnt take. Waited a week amd tried again.. I used lots and lots of action on the mouse with the tongs..took a long time but he finally took it.
Be persistent. Make sure the f/t is warmed up at a good temp, either with a hair dryer or running it under hot water inside a ziplock baggie so it doesn't get wet. If he is still refusing after a few attempts, I have heard of people splitting the skull a little to help entice the feeding response.