In any action against an unauthorized insurer pursuant to section 20-403, if the insurer has failed for thirty days after demand prior to the commencement of the action to make payment in accordance with the terms of the contract of insurance, and it appears to the court that the refusal was vexatious and without reasonable cause, the court may allow to the plaintiff a reasonable attorney’s fee and include such fee in any judgment that may be rendered in the action. The attorney’s fee shall not exceed one third of the amount which the court or jury finds the plaintiff is entitled to recover against the insurer, but in no event shall such a fee be less than one hundred dollars. 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.