The first argument you're passing to writeCSVfile does not appear to be what you're expecting in that subroutine.

Or at least it looks like you're mixing up $flatfile, $filename and $linename in several places.

also a couple of useless things that are in your code:

 @flatfields = ("$sys_time", "$consent", "$user_name", "$company", "$u
+ser_email");
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is the same as

 @flatfields = ($sys_time, $consent, $user_name, $company, $user_email
+);
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since those values are already strings (and even if they weren't, perl will convert them for you when you treat them as strings anyway).

And map{} does a local $_ already, so there's no need to do an explicit local $_ in your code.

So taking all that in account, you may want

$linename = join(",", map { s/"/""/g; qq("$_") } $sys_time, $consent, 
+$user_name, $company, $user_email);
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instead.