I have paid off and received the title to my car. Six months after the account was closed, I receive a letter that says an error was made, re: paymt

I financed a car through Chase Auto Finance in Feb 2007. In the early part of 2011, I had sent a payment through Western Union to Chase to satisfy a payment. In June 2011, I came into some money, and I was able to pay off the rest of my money owed, which released the lien, and the car became mine. I received a letter stating the car had been paid off, and I had also received the title, which is signed to my name. Earlier this month, I get a letter from Chase saying that Western Union had made a mistake and sent the my payment through them twice. Therefore, the amount I was quoted when I paid off my car was less than was actually owed (although it did not show in their computers at the time). So now they have reopened the account, and demand payment for the amount, which was in error. My question is this: do I owe them the money? They quoted me the price to pay off, told me the car was paid off, and sent the title. The error was on their end. Do I need to pay for their mistake?