The drop-down for the quantity of the product on the cart page is limited to 1 - 10 by default.
There are two ways you can increase this number:
1. You can set the Maximum Quantity for a specific product: https://docs.woocommerce.com/document/minmax-quantities/
2. Add this to a child theme's functions.php file, which will change the maximum number in the dropdown for all products without a specifically configured max quantity:
add_filter( 'vamtam_cart_item_max_quantity', function( $quantity ) {
return 12;
} );