When Israel attacked the hill country against Moses' warning, who routed them as far as Hormah?

Answer: Amalekites and Canaanites

Though neither Moses nor the ark left the camp, they went up anyway, and the Amalekites and Canaanites routed them all the way to Hormah.

“But they dared to go up to the ridge of the hill country, though neither Moses nor the ark of the covenant of the LORD moved from the camp. Then the Amalekites and Canaanites who lived in that part of the hill country came down, attacked them, and routed them all the way to Hormah.”— Numbers 14:44-45 (BSB)