Wrong mailing address again!

My company is housed in a small, old four storey building.  Me and the other guys are usually in the second floor, and nobody is in the first floor.  On top of this, there wasn't a doorbell until a couple of weeks ago, so each time somebody came to our place, either they call us by mobile, or if they don't know our number, they just leave us a note... even though we're upstairs!

This usually used to happen with messengers.  They leave us a note on the door, and then we have to go in person to the post office to collect the envelope or parcel.  Yeah, this sucks so we got a wireless doorbell, and it's really neat!

But so far in just a couple of weeks of use, we've already found the mailman trying to leave us registered mail that doesn't belong to us!  The street address is correct, but the name of the company and the name of the person are wrong.  I don't understand why.  Just a few minutes ago I rejected some big envelope from Japan.  Only the street address was correct.  The company name, the worker name, the phone and fax numbers were incorrect.