You have a couple of typos - have a look at Use strict and warnings

my @files = glob "$calls_dir/*.hmtl"; # should be $call_dir and 'html'

I don't think this does what you think

$tidy->parse( $file, $contents_of_file )

From the docs :

parse( $filename, $str [, $str...] ) Parses a string, or list of strings, that make up a single HTML file. The $filename parm is only used as an identifier for your use. The file is not actually read and opened.

Try instead

 open my $in_fh, '<', $file 
    or die "Could not open $file : $!"; 
  my $contents_of_file = do { local $/;<$in_fh> };
  close $in_fh;
  
  $tidy->parse( $file, $contents_of_file )
      or warn "Error parsing $file :$!";
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poj