foreach loop excluding a catagory

I am trying to exclude a filter from a post. The theme I am using has the following code

// Get the filter > Category of item
	$catz = wp_get_object_terms($post->ID,'filters');
	foreach($catz as $cat) { 

		$currcat = $cat->slug;
		$catname = $cat->name;
		break;
	}

I have tried putting putting an if ($cat = -20); to exclude my filter id, but it didn’t work. Also I tried (‘exclude=20&title_li=’) after filters, but that didn’t work either. This is the custom query

$args = array(
	'post_type'			=> 'portfolio',
	'posts_per_page'	=> $counter_folio,
	'paged'				=> $paged,
	'order'				=> 'DESC'
);

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I thought I should put the exclude in this section of the code but it didn’t work either.
This is a template-portfolio file.
thank you for your help.