Sometimes you might have some issues connecting to battle.net.
In most cases it can be solved by just waiting from 5 minutes to around 1 hour or something like that. It differs from case to case but this doesn't always help, some of you might still not be able to connect.

There is a fix for it and you can find it in the link below.
The link works for diablo 2.
https://us.battle.net/support/en/article/battle-net-connection-issues