Wow. I am sorry you have to deal with this. I wouldn't let it go. This will set precedent, and they may feel free to treat you with the same disrespect in future exchanges. Maybe telling them just as you have told us from your perspective what happened will make them realize that they were asses to accuse you. If not, then at least they'll have an idea what is going on next time they're rude, and you terminate care.