Amazon Double DIp

Hi,
I would like to know whats your excuse when doing DD?
I have done the replacement and did try to get the refund now.
I'm saying that I didnt receive the item, but they said since the replacement already done, they need to investigate this.
the other time, I'm saying I receive the wrong item, they want me to return in back.
Lastly, the on the other account, Im saying that the box was empty, they also wanna start the investigation.
Can you guys please help me with this?
Or does the investigatin really must be done for the DD?
Thank you guys