Any due assessment levied in a specified amount under this chapter shall constitute a personal debt of every person so assessed or who owes such amount and it shall be due to the Commission when payment is called for by it. If any person fails to pay the Commission the full amount of such assessment when due, the Commission is authorized to add to such unpaid assessment an amount not exceeding ten percent to defray the cost of enforcing collection. Upon the failure of such person to pay any such assessment, the Commission may bring a civil action against such person in a court of competent jurisdiction for the collection thereof, together with the above specified ten percent thereon, and such action shall be tried and judgment rendered as in any other cause of action for debt due and payable; provided, that any producer may, if dissatisfied with any assessment that has been levied and collected, be refunded the full amount of such assessment provided that demand for a refund is made in writing and in the hands of the Commission and the chairman of the commodity board within thirty days from the date upon which such assessment was due, and that such assessment was properly paid and receipt issued prior to this date; provided, further, that the payment of the assessment is not the result of legal action brought against such producer; provided, further, that no such assessment shall be refunded to any out-of-state producer.