your website customizations do not look to be mobile friendly. and you have errors in your HTML.
you'll need to a) update your custom header, custom footer, and b) correct all of your customizations with HTML errors in them.
for A, you can disable viewport at Control Panel > Primary: Advanced settings > Disable Viewport
this will prevent your screen from rearranging things on mobile devices. and they will be locked in to a minimum with of 600px or similar. I don't remember the exact width, but it's a feature toggle that was added for sites that are in transition or that don't want to support layouts for mobile devices.
Last edited by isaac; 06/24/20199:58 AM. Reason: added screenshot of site with viewport disabled
