Any purchaser or beneficiary may, upon written demand of any cemetery authority, demand that any prearrangement contract with such cemetery authority be terminated. In such event, the cemetery authority shall, within thirty days, refund to the purchaser or beneficiary fifty percent of the moneys received less the contractual price of any merchandise delivered or services performed before the termination plus interest earned. In any case, where, under a prearrangement contract there is more than one beneficiary, no written demand as provided in this section shall be honored by any cemetery authority unless the written demand provided for in this section shall bear the signatures of all of such beneficiaries.