The secretary, whenever such an assessment is made, shall immediately notify every policyholder in such insurer either personally, by agent, or by letter directed to the policyholder’s usual post-office address, stating:
(a) The amount of the loss.
(b) The sum due from the policyholder as his share.
(c) To whom such payment is to be made.
(d) The time when the payment is to be made. Such time shall not be less than thirty days nor more than ninety days from the date of mailing notice.