Friend took mobile phone without consent,refusing to return what to do

I stayed in Vidyavardhaka Boys hostel, this happened 6-7 months back. A guy who was my branch mate i,e Mechanical stayed in the same hostel . He took my mobile when I was not in the hostel and later when I asked him he agreed he has my phone , when I asked to return he started giving dumb reasons such as he has given to his friend for repair, the mobile was slightly bent but I never asked him to get it repaired, I asked not to repair and get it back, I was happy with it ,it was running fine. he said after few days that his friend tried to remove the bend and phone's motherboard damaged and when I asked to replace it he is refusing and avoiding me. How can he take my phone without permission? Why will he repair my phone? One more info, He asked me to sell the phone( Xperia Z1 Current MRP 13000) for hilarious 1000rs because the phone was bent , I refused . These incidences clearly made me believe he deliberately stole my mobile and what he was telling was cooked up