Overriding a core module in a custom module

[Guest]

Hi, I am trying to override the contactform module's main php file from another module, but the override is simply not taken into account.

The structure I am using is: my-module/override/modules/contactform/contactform.php

Inside this file is the following code, but it is not executed (die()ing it doesn't do anything at all):

class ContactformOverride extends Contactform implements WidgetInterface
{
    public function renderWidget($hookName = null, array $configuration = [])
    {
        $this->smarty->assign($this->getWidgetVariables($hookName, $configuration));
        return $this->display(__FILE__, 'views/templates/widget/contactform.tpl');
    }
} 

Can anyone shed some light on where the problem could be?

Thank you.