Proving you didn't receive something at an address you don't live at will be difficult at best.
You're just in COFP territory, £100 & 3 points. However should you take this to court and lose you would likely see 6 points, a fine of a weeks wages and prosecution costs.
How confident are you that your testimony that someone else said they didn't receive it would be accepted? You would only see the mail you were given by the occupants so you personally couldn't say it wasn't delivered.