Releasing and final settlement

Dear Sir, i worked for a company for more than 14 years, I resigned my position through the official system, and the email mentioned the last working day as 20 days from my resignation date, the actual notice period is 3 months, but as per policy and as understood from HR during discussion last working day will depends on manager. After some discussions my manager approved my resignation, later I received an email from HR that mentioned i needed to work the 3-month notice period. i was moved to a new job after 20 days as per my plan. I sent a reply to HR mail mentioning that " My manager already approved my resignation with proposed last working day, then the remaining is only further process of settlement from your side then why i receive this type of threatening email, cc to my manager, country head and segment head. i did not receive any response from them. later after 1 month i received an email from HR mentioning that to join duty and complete the notice period otherwise they would take disciplinary action as per business conduct guidelines. after that, i send the same reply as earlier for the second mail also. It's almost 3 weeks, and till now no reply from them. Currently, my notice period of 3 months is also completed but i did not get my relieving letter and settlement. please suggest me the procedure to file a harassment case on employeer.