Is it time to worry after six days and no sign of delivery?

Stuff gone the same day has arrived, so has stuff sent later.

Sent out 17 parcels last week, so far so good except one.

What the hell happens to these parcels? It’s sat somewhere with a full address staring someone in the face. I mean the thick black ink can’t fall off.
So when I put a claim in do they actually look for the package first as I’d rather have that back than the £30 I’ll get tops.

Edit, things can’t dissapear the post office have it or one of their employees have stolen it.