We usually state that we are no longer able to service your account. It's interesting because many times those are doing illicit activities know the drill and don't complain.
Precisely the point. If you've decided to close the account because of activity in the account of one sort or another, the customer has probably been asked or talked to about the activity already. So when your Good-bye letter arrives, they probably know why. Providing reasons in the "It's over" notice only gives them something to push back against. It's not necessary, and it's not advocated.