Getting crazy with WooCommerce plugin

Dear Sirs,
Over the years you provided excellent solutions to a series of problems I had with Envato. Now there is one quite hard to solve.
Recently, a new law in Italy forced to adopt a method to create “electronic invoices”, so we had to install a new custom-made plugin (WooCommerce Fattureincloud Premium) that would send clients’ and orders’ data from WooCommerce to an external service able to generate and handle those “electronic invoices”.
This plugin adds a series of fields to the “Checkout” basic WooCommerce page, and the problem is that those fields are scattered randomly among the others, instead of being orderly put at the end of the series.
This problem happens with our Envato theme, while with other themes this won’t happen.
I have contacted the developer of the plugin, and after a series of unsuccessful modifications, he said it’s a problem of the Envato theme, not his plugin’s.
In the private content section of this post you will find the login credentials to my site, a couple of screenshots showing the problem and the PHP file modified by the plugin developer that didn’t solve the problem
Thanks for your help!