Should I Have to Pay for Unrecieved Treatment for my Braces?

My sister and I both have braces but my family is going through a hard time trying to pay the braces off. We recieved a letter in the mail saying that if we could no longer afford to pay them, make an appointment to have them taken off. My mom called and not only was the people she talking to extremly rude, but they said if we took our braces off we had to pay the rest of the money for each of our braces. Is it right that we have to pay money for treatment they didn't give to us?