Employer not accepting resignation and not giving relieving letter

I have worked in an one organization for 3.4 years, with discussion with HR I have sent my resignation mail to HR and management. On very next day they said we have relieved you from the company and you will receive your releiving letter via courier. I have asked for the resignation acceptance and notice period but they said no need of that. I trusted their words and left the company. After that I haven't received any documents, then I called to my HR but he not answered me properly. Then I called to the director of that company regarding my releiving letter, but he refused to give and threatening me like we won't give anything to you even resignation acceptance also. I went office to meet HR regarding this, but he haven't allowed me inside the office. My new employer asking relieving letter for joining but my ex employer saying like this. How to solve this problem ? Please help me