Found Boost mobile iPhone 5c, want to activate but I can't

My aunt found an iPhone 5c that i would like to use as my phone. It was found two months ago and was factory reset shortly after found. I went to go try and activate it at my local boost mobile store but was unable too.

The phone is apparently still linked to this persons account and the man at Boost Mobile said I needed the 4 digit pin for the account accociated with the phone activation to switch it over…

Is there any way i can completely wipe out the phone as if it was fresh out of the box and associated with no one? I have a boost max and i literally can't stand the size of it and would be happier with this small phone lol.

and no there's no way i can try and return the phone to its original owner because there were no contacts or texts on the phone when i received it
plus we're in a city 5 hours away from where it was found!

Nothing you could do. ICloud Activation Lock would prevent you anyway.

So why was it "factory reset shortly after found"?