37 C.F.R. § 2.209

(a) The Director may refund any fee paid by mistake or in excess of that required. A change of purpose after the payment of a fee, such as when a party desires to withdraw a trademark application, appeal or other trademark filing for which a fee was paid, will not entitle a party to a refund of such fee. The Office will not refund amounts of twenty-five dollars or less unless a refund is specifically requested, and will not notify the payor of such amounts. If a party paying a fee or requesting a refund does not provide the banking information necessary for making refunds by electronic funds transfer (31 U.S.C. 3332 and 31 CFR part 208), or instruct the Office that refunds are to be credited to a deposit account, the Director may require such information, or use the banking information on the payment instrument to make a refund. Any refund of a fee paid by credit card will be by a credit to the credit card account to which the fee was charged.

(b) Any request for refund must be filed within two years from the date the fee was paid, except as otherwise provided in this paragraph. If the Office charges a deposit account by an amount other than an amount specifically indicated in an authorization (§ 2.208(b)), any request for refund based upon such charge must be filed within two years from the date of the deposit account statement indicating such charge, and include a copy of that deposit account statement. The time periods set forth in this paragraph are not extendable.