Hey there MrJohnBBQ,
Your issue is definitely different than what the OP was encountering, since yours is happening on the Battle.net app itself rather than after launching the game.
It sounds like either a firewall is blocking the connection, or perhaps your internet provider is having issues connecting you to the Battle.net servers. You mentioned configuring the firewall, is that the built in Windows firewall you checked? Or are you using a third-party or hardware firewall?
If you are able to try connecting through a mobile data connection or through a VPN to see if that allows Battle.net to connect, that might help narrow things down further to determine if the problem is only happening on your home network with the main ISP connection.