What are my rights to fight contract terms that were not disclosed to me and incomplete information was given?

If the new contract or contract addenda you signed contained the term extension in reasonably plain language, then you probably have no recourse--people are bound to the terms of the contracts they sign, and are therefore required to read those contracts prior to signing. If they choose to sign without reading them fully, that generally does not absolve them of their obligation--therefore, whatever the sales person stated or represented to you, you were expected to review the contract before signing; if the term was right there for you to see if you had reviewed it, you cannot now complain that you did not see or understand it.

If the contract did not contain that term when you signed, you would not be bound. Or if the term was unclear, you may have grounds to challenge it if there is another reasonable, alternative interpretation.