what we can do if a customer says that he received a different item even after getting the exact item he ordered ?

Here’s some customer fraud news from f Amazon, Flipkart online shopping

https://www.businesstoday.in/current/economy-politics/delhi-man-cheats-amazon-166-phones-refund/story/261811.html

https://www.deccanherald.com/city/flipkart-cheated-rs-156-cr-proxy-customers-673885.html

https://www.indiatoday.in/technology/news/story/2-students-cheat-flipkart-of-rs-1-05-crore-152-premium-phones-357859-2016-12-16

https://www.indiatoday.in/technology/news/story/flipkart-delivery-boy-replaces-12-iphones-with-fake-ones-327220-2016-07-04

https://www.indiatimes.com/technology/news/a-21-year-old-cheated-amazon-of-rs-50-lakh-by-claiming-fraudulent-refunds-on-166-smartphones-331464.html

http://www.millenniumpost.in/delhi/two-youth-arrested-for-cheating-amazon-india-by-refunding-orders-265940