Wheel thread broken, who’s to blame?

Hello, I don’t know so well about cars. Now I have the following problem: On 08.11.2010 I had an inspection on which the wheels had to be removed. I had the inspection done directly at Hyundai. Today I had my winter tires put on in a workshop. I wanted to have this done only at Hyundai, but was 20 euros more expensive. Now the workshop, where I had the winter kingdoms drawn up, said that with the left front wheel a It would have broken the thread. You would have noticed this already when disassemblying because the mother was harder to solve than the others. But you could tighten the mother still. It was also cracked when twisting tight. The master then advised me that I should have an appointment at Hyundai. So I called Hyundai and told them the problem. They told me that the workshop that put the tires on me was to blame and that I now have to pay for it myself. That would be almost 200 euros, since something would have to be expanded or exchanged. Now the question: Is this really so expensive and do I have to pay for it myself? Wasn’t it my fault or? Thanks P.S. I apologize for technical errors =)