karenarnold, it's people like you that encourage them to try to get away with stuff like this! If they tried to overcharge me at the beginning I wouldn't pay they anymore until it was all straightened out. I certainly wouldn't pay them anything after it was cancelled!
you need to harass them. Have a lawyer write a brief letter indicating that they have violated their terms and that you will see them in court. The best thing for you is that it is pretty clear that they were REFUSING to act in good faith when it came to the terms of your agreement. Also inform them that you will contacting the state attorney general, the BBB, and the local TV station about your situation. That needs to be sent Certified Return Receipt Requested to be opened only by the CEO of the company.
You will get a quick and satisfactory resolution for your trouble.