The law mandates the bank to require the borrower to obtain and maintain flood insurance for the life of the loan, and if the borrower fails to meet that requirement then the bank must force place insurance on behalf of the borrower. Your blanket insurance does not protect the borrower.
From page 37 of the Mandatory Purchase Guidelines:
If the borrower fails to purchase such flood insurance within 45 days after such notification, the lender or servicer shall purchase the insurance on behalf of the borrower and may charge the borrower for the cost of premiums and fees incurred by the lender or servicer.
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The opinions expressed are mine and they are not to be taken as legal advice.