Goodfight,
Do you have a lawyer? Even a written agreement of some kind? Something that would take the heat off of you each and every month about whether or not he has taken care of his responsibility? He may actually be using this bill as a way to maintain contact and "control".

I have no idea what this bill is or what it is about, but could it be seperated? You are not his mother and you shouldn't have to remind him of his responsibilities. I think he's using it as an excuse. Find a way to block his play.