One Page Order Bug Fix Prestashop

I need urgently to fix a bug in One Page Order of Prestashop. I have an external shipping module, which doesn´t update it´s carrier cost when I change/add/update delivery address. Plus sometimes, when I change adress, I receive a technical error. I do not know what all to fix, but posibly the theme template/JS/AJAX and my custom module. Expected delivery is next 48 hours. Thank you.