I switched from T-Mobile two months ago.  For the second time they have sent me a demand for an overdue balance of £33.21.

"For service to be restored, please pay the amount in full stated at the top of this letter."

Of course, I don't want the service restored. (Actually, in a better, contract free world I probably would as O2 sucks, but that's another matter).

The letter continues;
"If you do not pay.... your account will be passed to a Debt Collection Agency" (aka Gangster Thugs, fronted by a Call Centre with profits creamed off by a smooth solicitor).  "Blah, blah, etc blah."

I'm sure I don't owe T-Mobile money.   But the last thing I want is a bad credit rating...

Then a second sheet of paper falls out of the envelope;

"ignore this letter and accept our apologies.

Yours sincerely,

Customer Finance"

In the future, when Capital Punishment has been restored, and computers administer all justice, when you receive a letter telling you that you will hang tomorrow... before panicking, just shake the envelope to make sure an erratum slip isn't lurking in there - "ignore this letter... with best wishes from the Public Executioner."