During the migration of accounts from IBLLC to IBKR Singapore, we assign a new account number to clients and the old account is closed. To retrieve statements prior to the migration date, clients must log into Client Portal with the old account's login credentials (username and password combination).
A closed account will still have access to Client Portal, where you can download closed account statements for up to the last 5 years by selecting the Performance & Reports menu followed by Statements under Reports.