A few years ago our friend (the one with the half-brain cat) got a letter from the Council saying she hadn't payed any council tax for an address she and her hubby lived in about 15 years ago.
She went hunting about the house, pulled out the council tax book in question and found that she did infact pay it.
So the next day she went down to the office and showed them the book. Needless to say they were gobsmacked at seeing the relic :-D