AIBU? Neighbour parcel delivery...

[Loveandstuff]

We had a new neighbour opposite to us move in recently. One day, Royal Mail knocked on our door asking us to take in a parcel for them as they were out. That was fine. But, 3 weeks went by and their parcel was still by our front door. I mean, WTH? I was being stubborn as I believe it’s their responsibility to pick their parcel up. She came to the front door and said (in a rather snotty way), ‘You have our parcel, I think it’s been here for awhile’.
How is it my responsibility to deliver it to them? AIBU? What do other people do?

I generally don't mind doing it (I have refused on occasions where it's something too big for me to store safely with my plonker dog and kids running around) as an aid to the courier guys who really have crappy working conditions to save them a redelivery run - but when I've spent a couple of days trying to get something passed on and having to keep an eye out and them being in and ignoring the door - goodwill wears a bit low at times.