Department not ready to releave after serving notice period.

I have joined in a private hospital in HR department. I have completed my one and half year or service over there.My department HOD is not accepting my resignation both in mail and company softwere also. As per my resignation my last working day was February second week. I have raised resignation after confirming with my reporting manager. At the time of payroll process HOD hold my previous month salary. HOD is not allowing me to leave the organization and not even releasing my salary also. Moreover HOD is threatening me by saying about my background verification in future. This HOD is intentionally giving mental harassment and gave instruction to the others also to torcher me. Not only me more than 7 employees left from the organization because the same HOD behavior. Nobody has the dare to escalate this things to top level management. What can I do against my current employer ? Is it affect my career as like HOD said? Should I have right to take any legal action against them? Can I take the legal action?