(a) Except for benefits payable under any workmen’s compensation law, which shall be credited against the personal injury protection benefits provided by subsection (f) of Kan. Stat. Ann. § 40-3107, personal injury protection benefits due from an insurer or self-insurer under this act shall be primary and shall be due and payable as loss accrues, upon receipt of reasonable proof of such loss and the amount of expenses and loss incurred which are covered by the policy issued in compliance with this act. An insurer or self-insurer may require written notice to be given as soon as practicable after an accident involving a motor vehicle with respect to which the insurer’s policy of motor vehicle liability insurance affords the coverage required by this act. No claim for personal injury protection benefits may be made after two (2) years from the date of the injury.

(b) Personal injury protection benefits payable under this act shall be overdue if not paid within thirty (30) days after the insurer or self-insurer is furnished written notice of the fact of a covered loss and of the amount of same, except that disability benefits payable under this act shall be paid not less than every two (2) weeks after such notice. If such written notice is not furnished as to the entire claim, any partial amounts supported by written notice is overdue if not paid within thirty (30) days after such written notice is furnished. Any part or all of the remainder of the claim that is subsequently supported by written notice is overdue if not paid within thirty (30) days after such written notice is so furnished: Provided, That no such payment shall be deemed overdue where the insurer or self-insurer has reasonable proof to establish that it is not responsible for the payment, notwithstanding that written notice has been furnished. For the purpose of calculating the extent to which any personal injury protection benefits are overdue, payment shall be treated as being made on the date a draft or other valid instrument which is equivalent to payment was placed in the United States mail in a properly addressed, postpaid envelope, or, if not so posted, on the date of delivery. All overdue payments shall bear simple interest at the rate of eighteen percent (18%) per annum.