Instagram fraud

I got scammed in instagram clothes purchase. the page name was pragati kurtis,they showed picture and vedios on Instagram and show that they have an offer 3 suits for 1500 so I buyed and payed in advance because they were not taking cod,so after a week they ask me for rebilling.they said me to pay more 2000 as there parcel seem to stick in some store house due to low amount issue,so I said why would I pay extra money to them.So I told them to cancel my order and return my money. even after that they were telling me same like rebilling karwa do , rebilling karwa do. I even told them that I go to police if you don't send back my money then they switch off their phone and private their insta account. I don't understand how those people scam others