Do you have anything in writing indicating they knew you were outside their region? I guess they could argue you didn't tell them in order to obtain a discount you were not entitled to which can be fraud. Maybe someone higher up found out about it and the people you worked with threw you under the bus to save themselves.
If the people you were working with were not, in fact, authorized to allow it but did knowing you were in CA then I don't think they could charge you. Just fire the morons that made the deal.

Did this company not have an office/region that covered CA? If they did, and you intentionally worked with another office in order to get the discount, you have a problem. I don't know if that necessarily is criminal but it does make you look guilty as hell.