I have tried selling off fake products showing originals

Hi, my name is vipul(16) and i am from Kota .. Actually i posted an ad on olx.in for my football shoes which was a replica model of the original one(₹26,995) for ₹3000.i didn't mention it in the description.I met a buyer who was interested in buying he was from Jaunpur,U.P. He didn't knew that it was replica he paid me ₹1500 on paytm on the day i courier it to him.And said that he will pay me ₹1500 after delivery.i gave him my aadhar .. he received and after 4-5 later he msg me that it is replica.Give me my money back.i will courier it back to you firstly i denied that i thought you knew it as the price was very low and it was an understandable thing.Later he said give me money back or else i will lodge an FIR.Then i said courier the shoes tomorrow I will pay you back he denied saying that i will not.Give ₹500 back or else i will lodge an FIR your career will be ruined and other things. All this chat was on Whatsapp.I paid him back ₹500. What should do now if he blackmail me later ???