Company not issuing relieving letter what can be done

I have resigned from my current company on 22th september 2016 . now as per their hr policies i need to serve 3 months notice period. i have already served 2 months of that now i wants to buy out my last month of notice period but they are saying that if i did that then they will file a criminal case against me as they mentioned in hr policies.earlier when i have joined the company the notice period was of 1 month and in last appraisal(april 2016) they changed that to 3 months and ask to raise any objection(if any) with in the 1 month of appraisal but since i have not read the document as i thought the hr policies won't be changed in appraisal change and hence i have not made any objection. now my new comapny asked me to join the company with in the 10 days and i am not getting what should i do next.please help