Applications for commission approval of specific new rates or charges or changes in existing rates or charges for telecommunications service which have not been heard and determined within six months and thirty days from the date the application was filed may be put into effect by the telecommunications company, in an amount not to exceed seventy-five percent of the total amount of the application, subject to refund of any amount collected in excess of the amount which would have been collected under the new or changed rates or charges as finally approved by the commission. The refund shall include an interest payment at a rate of interest determined by the commission, except that the rate of interest shall not exceed the overall rate of return which the telecommunications company is authorized to earn. When making its final determination on the application, the commission shall not consider the rates and charges of the telecommunications company put into effect pending such final determination. This section shall not apply to tariffs placed into effect under section 86-156.