Olx India — fraud . I paid all money through paytm and he haven't send me courier

I saw a ad on olx then i contact him he said he is from indian army and i finalised the deal over call after he told me that he will courier mobile phone and i have to pay half money before sending and half money .he provided me his Indian army canteen card as proof that he is not a fraud person .after that he sended me reciept of courier and next morning after the product reached i done the payment through paytm and after this when i paid whole payment then he started demanding for 4050 rupees as a security charges of a courier i told that i will not pay a single pie . I asked him to tell me their office location so that i can visit but they refuses . Then with the help of google i found the courier company contact no. And they told me that it is fraud many people are getting exploited daily through them and they said our company have no concern with them.
Kindly please provide me justice .