We have found that really high security settings within a network can block the necessary data ports that the sim needs to use. If you're on a home network, you can simply log into your router/modem, and set permissions for ports 9997 and 9999. Some routers/modems simply just have risk settings such as low/medium/high. If you're is currently set to high, try lowering it to medium.
Employer networks tend to have extremely strict network settings, so getting them to lower their security threshold to make ports 9997 and 9999 available for the sim might be a long shot, but if you have a tight relationship with your IT department it may be worth checking into.
If that does not work you will have to reach out directly to your network/internet provider and make sure they are not blocking any Ip's to your computer.
Here's a list of all of the IP addresses and ports that the simulator uses to pass data. You can work with your network provider to make your network isn't blocking any of these paths.
188.8.131.52/28 Sao Paulo
If after following these steps and you are still having issues please email in to firstname.lastname@example.org