Such a letter just happened to arrive a few hours ago - with the added benefit that when I actually cancelled my service and was told that only the latest bill had to be paid they ‘mistakenly’ also cancelled my mother's cellphone line (it was the same carrier).
When my daughter was one, our health insurance processing company cancelled the insurance on every child of all employees at my work. The next year, when my son was born, they cancelled my daughter's insurance again, because we had a new child now. They actually told us this on the phone. (I guess a lot of people must trade in the first child when they get a new one.) In each case it was actually pretty easy to fix, but it was really frustrating.