Postal Problems

This turned out to be a very expensive Christmas Card as I had to pay £5 to collect it from the delivery office.  It had no stamp on it. Then it wasn't delivered on the selected date.  The employee in the office told me it probably didn't get delivered on Saturday as they probably didn't deliver any letters on that day.  I had heard that if they were too busy the letters didn't get delivered.  How can that be? 1st class?  I think not.