repairs to almost new car

I'm new to doing this, so please be kind. I live in Ga. and have not had a car accident in 23 years. I was rear ended while driving my 2007 auto. I only have 13,500 miles on it and it doesn't have its first door andquot;dingandquot; yet. I have talked to the claims adjuster to understand the procedure to having my car repaired. I talked to two body shops today. One was on their andquot; approvedandquot; list and one was of my choosing. Both told me that the back bumper and one exhause muffler system has to be replaced. More damage might be expected when they take the car apart. I asked about replacement parts and both said the insurance company only want to use reconditioned bumpers. Isn't that wrong for a 2007 model car with the millage I have on my car? What recourse do I have before I choose to have it repaired. I'm not trying to get something better than what I had, but I don't feel I want something that might have been damaged and fixed either. Thank you for helping this old grandma.