Lantana and Yellow Bells Should Not Be Dead from Winter Cold

Q. I have had Tecoma stans, Yellow bells, in the backyard as well as lantana for the past 3 or 4 summers. They do well but never winter over. When I dig them up to replant, the root structures seem to be healthy and alive. The tag on the plant says they are cold hardy. Is there anything I can do to help them winter over?