Attorney General Mike Beebe says Arkansas CenterPoint Energy Arkla improperly billed customers for the state`s new sales tax on natural gas starting in February. The tax rate on natural gas went from five-point-one-two-five percent to six percent, but not until March First. Beebe said Arkla will have to credit bills or issue refunds for all customers statewide. The customers will not have to do anything to get their money back. Beebe said an alert businessman noticed the billing error and filed a complaint with Beebe`s office. It turned out that every Arkla customer in the state had the same billing error.