Except as otherwise provided by law, claims for refunds which are required to be paid by the Oklahoma Tax Commission shall be paid from funds in the official depository clearing account of the Tax Commission, derived from collections from the same source from which the overpayment occurred. Provided, in the case of refunds due to taxpayers who are required to remit taxes to the Tax Commission on a monthly or quarterly basis, the Tax Commission may, in lieu of such refund, credit the account of the taxpayer for such amount. If current collections from the same source are insufficient to pay refunds, available cash funds from the unclassified taxes account may be used for such purpose.