Employment Bond And Releving Letter

 I have been employed by an organization for the past 1 year. The company has a Service Agreement/Bond of 2 Years. Due to rotational night shifts and nature of job and recurring health and personal issues I decided to resign from the company. I was ware of the fact that I was under an agreement and would have to pay to get released. However when I communicated this to the company they refused to accept my resignation or either the penalty amount which was clearly written in the agreement. I need the releving letter from this company to even apply anywhere else. I\'m stuck and need a good advice on how to tackle this unfair situation. Please suggest.