[mothered]

so shall i reply and say it is my door but i hadn’t been contacted by the delivery person to inform me it has been left outside my door?

Do not give them any reason to decline the claim, so yes, tell them It's the door to your home and that you did not receive the package.

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the courier left the box outside my door

It was not personally handed to you, nor any member of your household so as far as you're concerned, the package was stolen at some time of the day/evening/night.