1. Sorry for the inconvenience, but I have tested your site on a mobile phone and the single product page layout is working and showing properly, please check this Gif: https://www.webmobilefirst.com/en/screencasts/A9O42rtYRQ/
It seems to be the cache issue at your end nothing else, please try to clear the cache of your site and check back again.
2. For changing the layout of the header in the mobile version, please navigate to Porto >> Template Builder >> Header and edit it with Elementor Page Builder, then you can change the layout as per your requirements, for the mobile version, please refer to this screenshot: https://postimg.cc/KKDK89pq