Endless looping of my life preview/ customizer.

Hi everyone, Ive been trying to fix this issue for so long and I am about to give up. I made a mistake creating my website https://www.nicolas.net.au modifying CSS straight on the editor not in a child theme. So I was planning to change my theme and kind of like start all over from scratch. When I try to preview my website in other themes It keeps loading and loading non stop. Obviously I can’t modified anything on the customizer area either.

Ive tried pretty much ever possible tool and advise available in forums and websites but nothing seem to work.

Upgrate WordPress recently, went to my cpanel and copied a fresh code for the customizer, tried different browsers, delete cache, deactivate and active my theme, change themes and nothing works.

Anyone? please this is turning so frustrating.

Thanks