Bake cake according to directions on the box. Remove from oven and immediately poke holes in the top of the cake with a drinking straw or chopstick to make holes for the caramel topping to sink into.
Prepare the caramel topping by mixing the caramel and sweetened condensed milk in a small bowl until well combined. Drizzle over the warm cake so it seeps down into the holes.
Measure out half of the crushed candy bars and sprinkle the pieces over the cake.
In a large mixing bowl, combine thawed whipped topping and softened cream cheese with an electric mixer on low speed until smooth and creamy. Spread mixture over top of the candy. Sprinkle remaining candy pieces on top.
Place, uncovered, in the freezer for about an hour; then place in the refrigerator until ready to serve. Refrigerate leftovers.