If your game is having trouble making and maintaining a connection to our servers, here are a few common solutions you can try:
If you are using a computer, you may need to disable your antivirus software and/or your firewall to allow your game to connect to the internet.
And If your antivirus software has already quarantined your game, you’ll need to go into that antivirus’s settings and un-quarantine it.
If none of those steps work, make sure that the following ports are open on your firewall and router: 80, 443, 843, 38202, 38203
You can test the status of those ports here: http://www.yougetsignal.com/tools/open-ports/
To open those ports on your firewall, reference this article. Choose your OS from the drop-down menu: https://us.battle.net/support/en/article/7842
To open those ports on your router, google or web search the brand of router you have. You should find straightforward instructions on how to access that brand of router’s administration page, and how to open ports while you’re there.
Additionally, try getting onto or off a VPN if you have one in use or no other steps apply.
You can also try switching between a wired ethernet and wireless wi-fi connection(as well as try setting up a new wi-fi network too).
And as always, you can submit a support ticket for additional help.