You're clobbering %rets. You should instead do:

$rets{"$retid$fnum"} = {
                 FNAME             => $fn,
                 RECLEN            => $rl,
                 LIAISON_EMAIL     => $mle,
                 LIAISON_FNAME     => $mlfn,
                 LIAISON_LNAME     => $mlln,
                 LIAISON_AREACODE  => $mlac,
                 LIAISON_PHONE     => $mlpn,
                 LIAISON2_EMAIL    => $ml2e,
                 LIAISON2_FNAME    => $ml2fn,
                 LIAISON2_LNAME    => $ml2ln,
                 LIAISON2_PHONE    => $ml2pn,
                 RETNAME           => $retname,
                 RETAILER_EMAIL    => $rce,
                 LIAISON2_AREACODE => $ml2ac,
                 RETAILER2_EMAIL   => $rc2e,
                 FTPCHECK          => $fc,
                 RETID             => $retid,
                 SCRIPT_NAME       => $scrname,
                 EXECFLAG          => $exec,
                 FREQUENCY         => $freq,
                 FILE_NUMBER       => $fnum
};
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Check out perldoc perldsc for more information.

I also noticed that you have if ($fnum eq "") { my $fnum = "_001" }. You are declaring a new $fnum that can only be seen within the scope of the if. In other words, $fnum will still be "" when you construct your anonymous hash. Perhaps instead you should replace the entire if with $fnum = "_001" if $fnum eq "";. I hope this helps you with your problem.