Try sales@stardock.com, support@stardock.com, or both. Try to not mention 'fuck you GPG/SD' if possible.
Here's my 1 bit of advice for you. If you are willing to put up with some troubleshooting, do so. Use the forum or support@stardock.com for more info. If not, go for the refund immediately as you will, without a doubt, have to do troubleshooting to get 5 friends playing together without issue. I've mentioned this before and I still think its a true statement - you can't expect to get 5 of your friends playing right after buying without doing some troubleshooting (port forward, reinstall, etc). It is what it is. Sadly, the game can be a headache. Your call, and I do not doubt for a second that they will gladly give you your money back if issues.
Do not even screw around - willing to try to fix, give it a shot. Not really - ask for refund, follow any troubleshooting steps they want you to do, then enjoy the refund if still having issues.
I CARE - BTW. I'm super