What is the punishment for breach of trust?

I have signed a contract with a company that offers post-placement payment options with a job guarantee. Their quality of course was not up to mark also when I try to communicate my issue to people there they told me you could not discontinue classes. In agreement they have written 80% attendance is required otherwise it will be a breach of contract. I left that organization within one month. They didn't provide me with any referrals or any help but kept my course access open. Now they are asking me to pay XYZ amount. I have not used their resources and also their resources and number of students in the class they promised were not the same. I have not used their resources and have informed them before leaving. But now they are asking me to pay very large amount of money otherwise they will take serious legal action against me. What should I do.