I've checked the software and the website and it appears that you can still download and install it. If you can't connect to their servers, then it means it's a problem on your side since the app is working just fine. I suspect this issue is directly related to the Windows Firewall or with the Internet Security that's installed on your PC.
I recommend turning them off or add the TomTom MyConnect to the firewall to allow it to connect to the Internet servers.
If you're using an older version of the software, access the following link to downloading the installation package for the latest version available: https://www.tomtom.com/en_gb/mydrive-connect/