Incorrect settlement quote

I had three months left, I requested a settlement amount and made payment. After the payment you inform me that the quote was incorrect and that I still have an installment due. How is this my problem if your system quoted incorrectly. When querying the amount on the settlement quote and the interest that was still more even when settling early, you were quick to reply to my emails now that I get no response to my emails. I want my account closed and the balance cleared as I paid the settlement quote as received.