Give them about a week to de-stress before you try again. The prey needs to be warm, dry, and moving. Once you've thawed them out and warmed them up to live-rodent temperature, run a blow dryer on the rodent's head for several seconds immediately before offering the prey on tongs. Living mammal's heads radiate more heat than the rest of their bodies and the snakes can sense this. Also maybe try thawed mice since they aren't going for thawed rats.
- Paul