Get ID and slug from taxonomy object

It sounds like you’re looking for the get_term_link() function.

Your code will look something like this:

<?php
$catid = get_sub_field('selected_category');

$term_link = get_term_link( intval( $catid ), 'product_cat' );
?>

<h4><a href="https://wordpress.stackexchange.com/questions/95584/<?php echo esc_url( $term_link ); ?>"><?php the_sub_field('title'); ?></a></h4>

As you can see, get_term_link() takes two argument, the term and taxonomy. If you’re saving the term object in the field and passing it as the first argument, then the second argument is optional. If you pass the ID, as done above, then you have to pass the taxonomy name.