Sorry to hear of the problem you are having.
Please don’t share sensitive information on the forum as this is public forum so the information shared can be misused by others.
Please change the shared credentials ASAP.
If you want to share anything privately then you can do so by adding them in the box having text “Enter your private content here (only you and forum moderators will be able see it)”.
I logged into your shared site and tested the theme customizer which is working fine for me.
Could you please tell me a bit more in detail exactly what issue you are facing so that I can help you?