Rear Suspension Coil Springs problems of the 2007 Toyota Prius

Driver rear coil spring broke. One end of it seems to have a chunk broken off. I have the coil spring. I had the dealer replace the spring so I do have repair invoice. I noticed the car sitting low on driver's rear corner while sitting in my garage. I have an identical model, a 2009 Prius, sitting next to this affected car, (a 2007 Prius). The garage floor is a flat concrete slab.