You should have tweak the husbandry first (always make husbandry changes before prey changes).
Now you just gonna have to be patient it may switch in a week, a month, a year it will it is own terms just be consistent with the way you are offering.
You can also offer a live rat half the size of what you usually are offering followed by a F/T (half the size of what you usually offering) soon as the first rat is down, sometimes the feeding response will be strong enough that they will get fooled and take the F/T when offered back to back (again simulate the movement of a live rat as explained above). If you are lucky it will take to preys down if not you'll have to use tough love which can only be done if the animal has a good body weight.