If you encounter issue when using Battle.net functionality we recommend that you contact the official support for the game:
Classic Games > Technical
You will have the option of filing a web ticket, or (depending on time of day and region) you might be able to request a phone callback or live chat support to get assisted with your issues.
You also have the option to 'Ask the Community' by using the forum link below:
A common error that you might encounter indicates game ports 6112-6119 being closed:
Your Internet connection is either very poor or is not processing UDP packets through port 6112. You will be able to chat but will not be able to play games. Contact your internet service provider or your system administrator for assistance with opening this port.