Hmmm ok, I’ve logged in and it’s still showing the admin as broken and the original theme as version 4.2, but I notice you said you’d reverted to the older theme above. The latest is 5.5. You’ll need to download a fresh copy of the theme from your themeforest account, this will be the latest version 5.5.
If you’ve saved all of your css changes in the child theme, then these will be fine when you upgrade (its only if you’ve made changes inside the main themes style.css that get overwritten). However, as you have multiple copies of the theme installed, with the same name that’s why it’s probably not picking up the child theme data, so clear out the ones you don’t need and leave only one child theme and version 5.5 active.
The child theme must be the active theme in the admin once the new version is installed to see the changes. Make sure your versions numbers in both stylesheets are 5.5. Of course you can saved everything to your local setup from the server before making changes so that you have a copy of everything should something go wrong and you need to go back.
Let me know once that’s done and I’ll take a look to check if the responsive.css is working as expected.