It depends on the variety as, while many will cope with cold down to -25C, not all clematis are even frost hardy.
If it isn't tender and you planted it deep enough and gave it food and made sure it was never thirsty then new shoots should appear in the next few weeks You could try giving it a boost with some liquid rose or tomato food.
Once it does start to grow, give it a slow release feed of pelleted chicken manure or blood fish and bone mixed lightly in to the soil around the base of the plant but being careful about damaging mor enew shoots coming through. Water it well and then mulch with compost and scatter a few wildlife friendly slug pellets as slugs love new clematis shoots.
