If a return required by this chapter is not filed, or if a return when filed is incorrect or insufficient, the appropriate state agency shall determine the amount of tax due. The determination shall be made from all information that the appropriate state agency may be able to obtain and, if necessary, the agency may estimate the tax on the basis of external indices. The appropriate state agency shall give notice of the determination to the person liable for the tax. The determination shall fix the tax unless the person against whom it is assessed shall, within sixty days after the giving of notice of the determination, apply to the director of the appropriate state agency for a hearing or unless the taxpayer contests the determination by paying the tax, interest, and penalty and timely filing a claim for refund. At the hearing, evidence may be offered to support the determination or to prove that it is incorrect. After the hearing, the director shall give notice of the decision to the person liable for the tax. The findings of the appropriate state agency as to the amount of fuel taxes, penalties, and interest due from any person shall be presumed to be the correct amount and in any litigation which may follow, the certificate of the agency shall be admitted in evidence, shall constitute a prima facie case and shall impose upon the other party the burden of showing any error in the findings and the extent thereof or that the finding was contrary to law.