Missing letter not delivered by the Royal Mail

A letter has been sent out to me on the 24th January 2018 but I still have not received it. The Royal Mail delivers them to me. The sender sent out by the Royal Mail.

What is your experience with the Royal Mail?

Do you receive your letters on time?

I have to say that missing letters make me extremely anxious and worried.

Mostly, I am worried that a stranger could be reading a letter for me that contains private information.