No insurance company shall, knowingly, issue any fire insurance policy upon property within this state for an amount which, with any existing insurance thereon, exceeds the fair value of the property. If buildings insured against loss by fire, and situated within this state, are totally destroyed by fire, the company shall not be liable beyond the actual value of the insured property at the time of the loss or damage, and if it shall appear that the insured has paid premiums on an amount in excess of said actual value, the assured shall be reimbursed the proportionate excess of premiums paid on the difference between the amount named in the policy and said actual value, with interest at six per centum per annum from the date of issue.