Trouble With My 4 Tires...

Hi, I just found out that all four tires need to be replaced on my 2010 Mazda6. I only have 18,180 miles on it. I am having a lot of trouble getting warranty service from the tire manufacter (Michelin brand). I have gone to several tire stores, who sell Michelin tires, and I have been told that they know nothing about any warranty service that they need to deal with. I was told that it will cost me approximately $540.00 to replace all four tires. This is unbelievable and very upsetting to me... seeing as how I only have 18k miles on them. I have done continual tire rotation, as directed. I have always taken very, very good care of my car. To have to replace all four tires is a huge, financial burden to me. This is definitely something that I did NOT plan on having to do, especially with so few miles on my car. Can you please advise me as to what I need to do to get some help with this problem? I truly appreciate your time and help with this matter.