Complaint about threatening & not accepting resignation by HOD

Respected Sir / Madam, I, Ashutosh Sharma have been working as Assistant Engineer since 16 August 2015 in PRSS department in company "Wind World (India) Ltd, Wind World Towers, Plot No. A 9, Industrial Estate, Veera Near to Bhagwati House, D67, Veera Desai Road, Andheri West, Mumbai.” On date 29 December 2016, I had resigned from my services due to some family problems, requesting early release from the company. My immediate head, Mr. Sitaram singhal is neither accepting my resignation nor supporting me for early release from company. Instead, he is threatening me to not to provide relieving letter as well as to ruin my carrier. He is continuously threatening me by sending sms on my phone number since the day i resigned. I have already lodged a complaint against my manager to HR department of company but they are neither taking any strong action against him nor relieving me from company. I am a very stressed & afraid with the current situation. Sir / madam, Let me make this very clear that I'm only concerned with my early release from company, not with actions against HOD. Please suggest.