HR is not responding to my resignation

Respected sir, I am working in an NBFC for the last two years. There is no black records against me in work yet.,I am working as a customer relationship manager for these years so I have decided to make a career change., I asked hr for a recommendation letter for my studies. He didn't give me so I decided myself to leave the company (December 17th) When I mailed my resignation immediately he responded that my resignation is not accepted, without telling reason but next day he mailed me for asking explanation,that I have joined two NCD in different years one on 2018 and another on 2019.,that I have collected from an investor and cheated him...it is true that I have two NCD,but One from my previous savings and chit fund and another from my salary. One person who was my fiancee with whom my relationship broken and I stopped all communication with him. He had called to my office and one colleague in her personal number. She already have some issues with me. From his talk he claimed the fund is his own. In the basis of that phone conversation she had made complaint against me to HR head. HR head mailed me asking for explanation regarding this marking CC to our complaince head and chief executive officer,but to me.they didn't disclose the complaint source.,I have proved myself with all relevant documents.but after one week only I got the reality.,that such a complaint even a mail or letter was not there. Even I got her what's up chat with the said person..to whom she was asking for submitting account transfer proof,but he couldn't. She had discussion with hr manager and without any complaint or proof they had made allegations against me.now I have made complaint against to my fiancee and asked for the copy of the complaint letter and submitted my resignation also. But hr is not giving any reply to me. What I have to do in next. Please tell me