I’m having a similar issue. While messing around with the configurations on the Dashboard, I saw an option to change the URL for my main site and the Dashboard page. At this initial time they were the same; sharing the main site URL. So, I added ‘/wp-admin’ to the end of the URL for the Dashboard access. So now, I cannot access the Dashboard because I am immediately forwarded to the site which is currently ‘Under Construction’.
Somebody please help!
