My Company not releaving me even after serving 3months notice period

3 years ago

I have been working at the current employeer for past 6 years. I resigned in mid july and am supposed to be released at mid of october. Now that i have resigned they feel i have betrayed them in some way and are now harrazing me.
There is a clause in my contract which states "In the event you have an you having an incomplete assignment, the Company has the discretion to relieve you only at the end of the end of three months' notice or completion of the assignment". but the word assignment is not defined.
So they have given me a task which will not be over in 3 months i have officially raised conserns on this through mail. They say me leaving will incur losses of the amount of 20Lakhs and they asked me to pay it and leave. I have call recordings of these conversations.
And i have asked them for list of tasks to be done with in 3 months and before i leave with received no reply. What am i supposed to do i have job lined up which is expecting me to join right after i leave this company.