This Jeff person is a complete dick. You are best to not have any dealings with him. I think he's mental. I'm serious. Has he nothing else to do but send shitty emails to clients and threaten them with taking their children's "seats" away?
You did nothing wrong. You are the customer. You were upset. Any professional would have replied with an apology and verified the amount owed. Period.
So, wipe the dust from your feet, give a big sigh of relief you escaped from this mental case, and get on with your life. Heaven only knows what you saved your children from. God gives us signs; we'd best listen.
I agree -- he has nothing better to do than engage in name-calling and worse with CLIENTS??? Not very business-like. That alone would make me run screaming.