My friend signed a blank stamp paper from me and now blackmail me for more money even after I have returned more money to him.

Last year 2023 near year end I urgently need 4000 rs, my friend said that he will borrow from a person and will gave me(he gave me those money latter I acknowledged that). He make me sign a blank 20rs stamp paper. For months I have been returning him like 1000 per month. After that I again took 4000 from him. For months I gave him 3000,2000 as I can afford. I am a student and now he is asking for 15000+ money,when I asked him to show the calculation of the money as he said I have took, he failed. And now blackmailing me to gave the stamp paper to police. And also inherit my scooty. Only I have signed on the stamp paper with no eyewitness or lawyer not even his own sign. Tilled date I have returned him more than 15000 rupees, still he is blackmailing me, as an appearing student for government jobs, I don't want any legal case against me now. But I have become fed up by his blackmailing, almost every week he claims for money and now to cool him I gave 500 weekly to shut him. Even after returning such huge amount of money he is not returning my paper.