All returns required to be made by telephone and telegraph companies having their principal offices out of this State shall be made in such form as the department shall prescribe and the department may require answers, under oath, to any questions it may put to the principal or any other agent of any of such companies in this State and may examine any of such agents, under oath, relative to the property and affairs of such companies and the management thereof. The department may administer any such oath.
S.C. Code § 12-37-1990