Net::Telnet is not the command line, you can't specify the port with a space just because it works from the shell...

my $telnet = Net::Telnet::Cisco->new(
    Host => '1.2.3.4',
    Port => 2005,
    Timeout => 2,
    Errmode => 'die',
);
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Which is, of course, how the documentation would have told you to do it.