I am getting the impression that the seller fed live and you are attempting to feed f/t and they haven't eaten for you yet.
Am I correct in thinking that?
If so, it may take some time to get them to take f/t the first time. Leave them alone and don't handle them.
Don't offer them food every day. Offer weekly until they get hungry enough to eat.
After eating the first f/t, they should accept them readily from then on.