Costco Broke my wheel stud and will not pay to repair it! Raleigh, North Carolina

I took my Honda Pilot to Costco tire shop to have the tires rotated and they broke a stud. They told me they would reimburse me for the repair and even put this on my receipt but now refuse to take full responsibility for it!  They are only willing to pay 50% of the $438 repair.  I have contacted the home office and the store manager and have been given the run around and made to feel like this is my fault because I installed brakes on my vehicle 2 days prior.  There is no way that I could have cross-threaded the stud with my hand wrench. Who in their right mind would go through the pain staking trouble of cross-threading a nut the whole way on a stud after doing a brake job.  That would be like putting your brakes on upside down! Yet they claim that the stud was cross-threaded and it broke when they tried to remove it.  Any mechanic knows that this is just not possible.  They are unprofessional and rude and I will never do business with them again.  I suggest you find a reputable tire center to work on your vehicle and avoid Costco all together!