Should a Haram investment certificate be immediately canceled, or is it permissible to keep it to avoid the bank benefiting from a portion of the amount upon cancellation?

Investment certificates offered by interest-based banks are either a loan with interest or a combination of a loan and gambling, both of which are prohibited. As for certificates offered by Islamic banks, in accordance with Sharia (definition) principles for Mudarabah (definition) (profit-sharing), they are permissible, and their profits are lawful. If the certificates are from an interest-based bank, they are prohibited, and your unawareness of their nature negates the sin, but the contract must be canceled immediately, without waiting for its term to end.