All that message says is that $f22 = undef. Sometimes subs return undef in the case of errors. Because I can not see $f22 anywhere in the code you provided and my knowlegde of Tk is minimal I will stop my answer here. Hopefully it will get you a bit further until others appear.

Update: sorry I spotted my $id = "\$f" . $j . $c; # Create identifier

But you are overriding your identifier in the next line by $id = $frame->Text

Should you perhaps declare a hash before the loops and then save each return of $frame->Text() to that keyed on (ad-hoc) id names? For example:

my %widgets = ();

... # your loops

my $id = "f" . $j . $c; # Create identifier
my $awidget = $frame->Text(-height => 6,
                                -background => 'white', 
                                -width => 10)
                        ->pack(-side => 'left');
die "widget failed $id" if ! defined($awidget);
$widgets{$id} = $awidget;

... # closing the loops
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Then you can access f22 like $widgets->{'f22'}->insert()...

Update #2: $widgets{'f22'}->insert()... is the correct way to access 'f22' widget