I thought the point of COD was that you didn't get the package until you paid the fee.
The best bet is to take it to a service center and talk to a manager there. Let them know you refused COD (or the package was sent unsolicited) and that you are refusing delivery. Tossing it on your doorstep does not count as accepting the delivery, they just do that because it is cheaper for them.
If you want to game the system sign up for MyUPS so you get advance notice of all deliveries to you. Then when these unknown packages show up bound for you reject them immediately. That goes into the computer sorting system and can often get the package pulled before it even reaches your local service center.
She’s in Canada and it sounds like the packages were from US.