Automatic add product to cart if total weight more than 50 kg

Hi, hikashop team.

I have a problem with automatic adding a product to cart. I want to add product into cart when total weight is more than 50 kg. I found this plugin: https://github.com/RickR2H/hikashop-free-product , but this plugin doesn't function correctly. This plugin add more than one product into cart and removing product is not working. I want to change it according my needs. Why plugin add more than one product to cart and how to fix it? How to add product if cart weight more than 50 kg?

Thanks for your help.
Peter