What can I do if my auto shop does not want to take responsibility for over-torquing my wheel nuts?

My car started to make a strange low-clanking noise last week while on the way home from work. I had resolved that if it continued that I would see the mechanic shop that weekend to find out what was going on. The next day, while heading to work, I nearly lost my life on Route 222 as the result of my front right tire coming loose. After being towed to PepBoys, the mechanic their removed the hub and asked me if I had anyone work on my vehicles wheels recently.. I mentioned that I had a tire rotation a couple of weeks prior to the incident. He then said that he believed, based on the condition of the hub that my wheel locks were over-torqued and proceeded to show me why... I went back to the shop who rotated my tires in an attempt to get them to now reimburse me for all of the expenses associated with the tow and repairs, but they do not want to take responsibility for what happened. What can I do?