Unintentional injury to other person as a part of private defence

Sir, I and a friend of me were living in a room in a hostel. On 20th of this February, he slept around 10:30 - 10:45 pm in the night and was doing my work on laptop sitting on a study chair. So I told him that I will switch off the light after finishing my work. After sometime around 11:00 pm, he asked me to switched off the light, the I said I'll finish my work in a few more minutes. Then he immediately threw a steel glass towards me which narrowly missed me and came near me and started beating me (3-4 punches) with hand very hardly.The laptop fell from the chair and so I bet with the plank and as he hadn't stopped beating me, I use the chair as defense and onto which he tried beat again which cause him the injury to his right hand. He went to hospital and surgery was done for the misalignment of joint of little finger of right hand. Now his friend started to ask me to pay the amount or else they will file a case. Will there be any problem to me or what should I do now, sir help me..