The utilities are not in the Realtor's name and we really can't have utilities turned on or off without written authorization from the client (you). The utilitiy companies generally ask for a copy of that written authorization before they will let us do that sort of thing and are even asking for Notarized signatures on requests we Realtors put in lately. The thing to do now, is for you to have the utilies turned off.
As far as collecting for utilities you've accidently paid on the Buyer's behalf, I doubt it would be worth the legal hassles involved. You could always ask the Buyers though.