[mothered]

Is there a method I can use to refund the phone without it getting blacklisted?

You cannot do anything on your end.

The IMEI Is placed In a pool of blacklisted numbers by the company and when you attempt to activate with a given carrier, It will be declined. That's "If" they decide to blacklist It.

I was thinking of using DNA (if they didn't take a photo of it at my doorstep)

Obviously It was left at the premises without a signature?

or saying that the item was not in my package (because it's a light phone).

What's the exact weight of the phone?