Abused a person through messages. How to proceed ?

Few days back my friend name Nandu stole his roomate's book as it was his last day in Hyderabad city and i was with him when he was going. The reason he stole his book was his roomate took his book for a exam he was coming the day after he was going home. I dropped nandu till auto and he went home. Next day when his friend came he saw book was not there and asked me I said you took his book so he took your book. He called Nandu and asked him about him. Nandu said i don't have your book and blaming me for taking his book. I was very frustrated and messaged him personal things about his father and scolded him. After my message he texted me that he will going to file SC atrocity case against me bcoz of that message. I never used caste related things and not abused him racially. It was because he stole that book and blaming me for that. He said he will complaint on 16th June 2 days before our exam. Please help me how to proceed