In any such action against an unauthorized insurer, if the insurer has failed for 30 days after demand prior to the commencement of the action to make payment in accordance with the terms of the contract, and it appears to the court that such refusal was vexatious and without reasonable cause, the court shall allow to the plaintiff a reasonable attorney fee and include such fee in any judgment that may be rendered in such action, and in no event shall such fee be less than $100. Failure of an insurer to defend any such action shall be deemed prima facie evidence that its failure to make payment was vexatious and without reasonable cause. [PL 1969, c. 132, §1 (NEW).]