Perhaps it might be your internet provider? You might want to try changing your IP, using a wired internet cord, checking with your internet provider, restarting your router/computer/modem etc., uh... Maybe, if you need to, buy a new router/modem? (If you need to, but most likely not.)
Also, you can try "pinging" them.
If you're on Windows:
In the bottom left, go into the system thingy. At the bottom of that, type "cmd" and hit enter. It should open up something like this.
Type in "ping eu.mcgamer.net" or "us.mcgamer.net" or "eu1.mcsg.in" etc - One of the IPs for MCSG.
Post what you find?