Wis. Stat. § 24.22: Excessive payments to be refunded.

(1) Whenever full payment of the principal due upon any certificate of sale by the state is made subsequent to the payment of the annual interest on the principal, the excess of the interest so paid shall be refunded to the person entitled to the excess payment, from the proper fund, on the warrant of the department of administration.

(2) In the event of the double or erroneous payment of interest, charges, or taxes on any certificate of sale or loan by the state, the amount erroneously paid shall be refunded in the same manner as excess interest payments under sub. (1).