Amazon - Wrong AC delivered and not giving the refund

I have ordered * start lloyd AC from Amazon, they delivered * star AC and the brand engineer installed it too... when i noticed the wrong product , first amazon accepted and promised me to pay the differential amount of * star and * star of around **** rs.
For the return of item , no one came for pickup and now whe i left that place they are denying for paying the promised differential amount and asking me to return the item. I am in pune and package is in goa , i told them it will cost me **k to go back there to return and eàsy way would be to charge me for the * star which is delivered and not * star and pay me the difference. Got few arrogant agents who are not really providing any solution and disconnecting the calls, very frustrating service and mental torture from amazon. Kindly help me to file a legal case against amazon.