The Office of Regulatory Staff may, after due notice to officers or managers of the company, inspect the property, plant, and facilities of any telephone utility at any and all times and inspect or audit at reasonable times the accounts, books, papers, and documents of any telephone utility. For such purposes an officer, employee, or agent of the Office of Regulatory Staff may during all reasonable hours enter upon any premises occupied by or under the control of any telephone utility. An officer, employee, or agent of the Office of Regulatory Staff authorized to administer oaths may examine under oath any officer, agent, or employee of such telephone utility in relation to the business and affairs of such telephone utility, but written record of the testimony or statement must be given under oath.