As has been posted elsewhere, you're resetting the hash for each line you read - in addition to the other suggestions, TIMTOWTDI, so you could try something along the lines of ...

my %IACISBN_ENUM = map {
    chomp($line);
    my ($IacIsbn, $Title, $EPI, $BundleCode) = split "\t";
    (
        $IacIsbn => {
            'Title' => $Title,
            'EPI' => $EPI,
            'Bundle' => $BundleCode
        }
    )
} <FILE>;

close FILE;
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