Amit Kadam — taken money but not received any good

Sir,

I am arpit chaurasia of class 11th (Age - 17)
Actually i want a phone and i keep on searching a second hand phone because my budget is low as i am a student and i collect money and keep on saving it. So on quikr i found a man selling iphone 6s in just 17000/- or 18000/- so i contacted him on quikr itself so he told to message him on what's app so i messaged him on what's app and then we talk i little bit then we talked on a call then we decided to close our deal in 8000/- only...
So he said that send me money and i will send the phone by courier.
Sir i payed him 5000/- by paytm and 3500/- by bank transfer but i didn't receive any phone till now.
I didn't tell anybody in my house because of fear.
His name is "amit kadam"
Mobile number - [protected]
Lives in maharashtra

"please help me sir"

Thankyou