Just holding up to the unused phone number doesn't cost 20$ a month.
If you go VoIP, you can port your number for a couple dozen dollars max, and then have unlimited incoming minutes on the said number for under 6 dollars a month. (»
VOIP Tech Chat) Clearly the costs for simply keeping a number for a couple of months, when no actual service is provided, are practically negligible.
But here, again, we're talking about disaster victims. It's clearly unacceptable to be charged a "Vacation Fee" of 20$ pm when your whole residence is destroyed. It is obvious that procedures are missing and representatives are not trained.