Tenn. Code § 28-3-301
Notwithstanding any other law to the contrary, if kilowatt usage is inaccurately recorded or registered due to equipment failure and results in a customer being undercharged or overcharged, and the customer is unaware of the error, defect or failure, no utility district, municipality or electric company shall be authorized to collect or assess a charge for such usage, or to reimburse the customer for overpayment of such usage, prior to thirty-six (36) months from the date the error is discovered and billed; provided, that if a date certain can be established for such error which is less than thirty-six (36) months, no utility district, municipality or electric company shall be authorized to collect or assess a charge for such usage, or to reimburse the customer for overpayment of such usage, beyond such date.
T.C.A. § 28-3-301