If you live next door to the estate crime lords then you are unlikely to ever get your post.
I wonder if there's a way to tell Royal Mail that under no circumstances should they do this.
With regards to the postie already doing this, then yes, they've been breaking the rules unless you have a prior agreement for your mail to be redirected.
I should say that at my last address, the first time I ever met my neighbour, after five years, was to collect a parcel that had been left at their house.
I never saw them again, although I was there for another nine years...