CNA national Warranty Company changed warranty terms after contract was signed Scottsdale , Arizona

on 08/2005 I purchased a vehicle with 32021 miles from Jay Chevrolet the vehicle was covered under the manufacture warranty for 3/39000 it was stated i could purchase a service contract for an addional charge at that time i purchased  one for 60/75000 which costs me 2000 dollars and signed a contract that my vehicle was covered under warranty until  08/2010 or 107021 miles in 12/2009 my check engine light came on I took it to the dealer with 85770 miles  to find out my warranty had expired at 75000 miles and a letter was supposedly sent out  amending the mileage  which I was not aware of  nor did I get I contacted the dealer and cna all they said was if I want they will extend the warranty until 90000 miles if I want to pay 600 dollars why would i want to pay 600 dollars for less than 5000 miles when i paid 2000 for 75000 miles and in reality only got 36000 I paid for a warranty for the first 32021 miles and did not even own the vehicle cna is a total rip off but they had no problen taking my money I guess when you do business with cna thru the dealer a signed contract doesnt mean nothing  I guess they can change the term whenever they like and they dont have to notify you  nor give you the option of agreeing to the new terms I always thought when you signed an agreement or a contract it was a legal contract that could only be broken or modified if both parties agreed but with cna all they do is take your money and change signed contracts whenever they want what I ripoff beware of CNA NATIONAL WARRANTY GROUP  they will take your money and rip you off