Energy retailer AGL will be forced to pay a $30,000 fine for overcharging some Queensland customers.Department of Mines and Energy director-general Dan Hunt today confirmed the fine, issued earlier this week, would stand, despite AGL challenging the penalty.In March, AGL admitted it had wrongly charged pensioners the state's $98 annual ambulance levy and failed to pass on the $11 per month seniors' rebate on their electricity bills.The admission came one week after AGL and Origin Energy were found to have withheld a $55 annual gas rebate from 50,000 pensioners in the state.AGL said the fine was inappropriate, as only 250 customers were affected by the error.But Mr Hunt said the penalty was reasonable.Origin Energy and Queensland Electricity were fined $50,000 and $15,000, respectively, for similar breaches.The maximum penalty under the Electricity Act is $99,375 per breach. AAP