Threatening by a Guy

I am Assistant Professor by profession. one of my student who was very nice to me became very possessive and tried to control me afterwards last year in june. i immediately disconnected him from everything and asked him not to contact me in either way. at first he was okhi but later on tried contacting me and after 5 mnths left the university. since i locked all his contact numbers so i hardly had any conversation with him. but in march my be he started some job in call centre started calling me infinitely through different numbers and threatened me that if i didn't answered he will start defaming me over social platforms and will contact my family numbers and will threaten them so i finally talked to him. . At that time I didn't wanted any police interference. I thought, I am a teacher I have counselled many, I can handle that. I can counsel him but after almost two months of a lot of stress and hours of talking. he started blackmailing me, that if I didn't showed him affection he will kill himself. I am having recording of this conversation. I blocked him now from everywhere. Now again he started threatening me. What should I do. he is christian and from kanyakumari, Tamil Naidu.