Not an employee of Stardock, so please don't vent in my direction. Only trying to help. Also, a support person might see this thread before the natural course of things and reply earlier.
1. I'll bet as part of the purchase you signed a 'share with' or 'receive advertising or notices from' clause in there somewhere as a result of support for the game going through Stardock (maybe, just guessing). Maybe not.
2. Since you You bought the game on Steam, shouldn't your questions/anger (less productive) be towards them?
3. If you wish to unsubscribe and you received an 'error' message, email email@example.com and try to describe the situation objectively. Then, you will receive an 'auto reply' message, which is a receipt and ticket number. keep that as reference. You then should wait until you receive a response from an actual person before continuing to correspond. Not doing so will only cause your message to go to the end of the queue.
4. Stardock support works M-F, 9-5. Writing over the weekend won't get an immediate response from a support person. Wait patiently. After all, this isn't the first advertising you've gotten (from the tone of the OP). Mondays are usually hectic so it might be Tuesday before you hear back from an actual person.
5. Uninstalling the game would only be "cutting off your nose to spite your face"... you've paid for it, so why not enjoy? The rest of the stuff will get taken care of, so... have a better rest of the weekend.
Hope this helps a bit.