If you are continuing to assess interest charges on the account, even though matured, a literal reading of the regulations will give you that you still need to send periodic statements until you refrain from charging any fees or interest to the account.
(2) Periodic statements. (i) Statement required. The creditor shall mail or deliver a periodic statement as required by §1026.7 for each billing cycle at the end of which an account has a debit or credit balance of more than $1 or on which a finance charge has been imposed. A periodic statement need not be sent for an account if the creditor deems it uncollectible, if delinquency collection proceedings have been instituted, if the creditor has charged off the account in accordance with loan-loss provisions and will not charge any additional fees or interest on the account, or if furnishing the statement would violate Federal law.