You did one thing wrong.
It was not losing your serial number.
It was failing to register before losing your serial number.
I can open impulse, click on sins, and view my registration number any time I like. When i brought my expansions, my copy of sins was already in impulse, so i never needed my booklet again.
Hell, If my computer died, harddrive wiped, all i would have to do is go to another computer, install impulse, and BAM. I now have all my games back.
Stardock is very loyal, and a great company, and in no way intrested in making a quick sale. (they are sill updating SINS... its been 4 years since it came out now?)
Be a man, suck it up, and go to a store and buy 'trinity'. from your post you mention 'the expansion', and not 'the expansions' suggusts that you dont even have the full game. I have seen it for $30 bucks. Hell, you could just wait for a sale, it appears on sale on that impulse daily deal every so often, prolly could pick it up for $15 if your patiant enough. Hell, buy 2 so you can get a group of 4 friends together and do some 2v2 lanning. "one of the best multiplayer strat games of all time" is worth it.
Seriously. Your acting like a baby. Its like going to the hardware store and telling the clerk, "hey, I just brought some nails for my hammer which I lost 2 years ago, you owe me a new hammer, please."
seems harsh? ya, well sorry. My avatar is a ton of lead. you just got hit with it.