Speed Control Springs problems of the 2008 Buick Enclave

My husband, I, and our 3 young children were driving on I-94 at 70mph when our check engine light started flashing,the vehicle immediately starting shaking and riding extremely rough and the engine died. Fortunately we were in the right lane, and there was a wide shoulder for us to pull onto. We had the car towed to a gm delearship, who ran diagnostics and found that there were cylinder misfires on cylinders 1,3 &5. They ran further diagnostics and found that a valve spring broke & dropped into the cylinder. The piston hit the valve, knocked a hole in the piston, and pieces of the valve went through the engine. This vehicle was purchased 5 yrs and 9 months ago (9 months out of the warranty), but only halfway through the 100,000 mile warranty. We were given a gm customer service contact name (lashawn) and number, but she will neither answer her phone, nor return our numerous messages! we purchased this vehicle brand new and have done all maintenance work on schedule, and have never had a problem with this "luxury" vehicle. We chose this vehicle for all of its safety features, as parents of 3 young children, safety is of our utmost concern. We certainly didn't feel safe 3 hours from home, traveling back from vacation, in the middle of WI completely stranded with a vehicle whose engine died within 5 seconds of the warning lights coming on. As inconvenient as it is that our vehicle is 3 hours from us, we are so thankful this didn't happen in downtown chicago, where a dead vehicle on I-94 could have easily turned into a fatal collision.