You should let him get used to his new enclosure. Check if humidity and temperatures are correct. Keep trying every week. Offer live rat pups and leave it over night. Get a scale and measure his weight. If he's losing weight in a month, try assist feeding a few pinkies and then try a live rat pup the next week. I had to assist my butter for 8 months and I was getting ready to give up. But now she's eating on her own. She is now eating live adult rats on her own every week. It takes time so be patience.