Thank you for your response

I've just spoken to them and they advised its because the theme I am using is not mobile responsive and advised that I change the theme

Hi - I changed the theme to a responsive theme however half of the background (height) is missing from the mobile site. I asked SiteGround for help but they advised me to contact Weebly as it is a Weebly designed theme. I think they've given me the brush off but not sure if this can be easily fixed.

Background images are designed to fully fill whatever space they contain, whether it's the entire page for a splash back image or a section. The reason you see something different on a mobile device is because screen ratio is reversed from that of a desktop screen (tall vs wide).

When that happens you have two choices: clip the sides of the image so that it fills the space vertically, or fill the space horizontally without clipping, but with some empty space at the bottom.

The latter option usually looks worse than having part of the image clipped. Some people have made small CSS tweaks to either reposition the image slightly (to control what is clipped), or hidden the image entirely on mobile and used a solid color instead.

I don't know if SiteGround provides help with CSS, though we don't ourselves (we can't even access your account).