Payment of compensation

All sums of money payable for compensation under this Part shall become due three months after the claim for such compensation is made in respect of the stoppage, diminution or damage complained of and simple interest at the rate of six percent per annum shall be allowed on any such sum remaining unpaid after the said three months, except where the nonpayment of such sum is caused by the willful neglect or refusal of the claimant to receive the same.