Hello chokari
we tried resolving the issue but could not figure out what is causing the problem in customizer
So we switched the theme and activated a random theme and still the problem of customizer was there.
This might happen due to some changes in settings and due to so many plugins overlapping each others settings or this is a hosting issue
So you may contact your hosting provider for this issue to be resolved and another thing you could do is reinstalling your wordpress.
Which will eventually reset all the modified settings and then activate our theme on your website.
Thank you