Where does my ubisoft activation code come from

I sent him everything on and yesterday, when i tried to run AC4, i was asked again for the activation code, and when i inserted the code that i received from Steam i got a message informing me that my own key was in use on another account. On January 3, 2014, i asked for help on ubisoft support, after more than 2 weeks talking nonsense and almost insulting my reasoning someone with the name 'Tom', asked for all my uplay account details, including login, password, serials, and even screenshots of the steam transaction. On the first day of 2014 it got even worst, i got a weird message telling me that the game was running in 'LIMITED MODE' and since then i completely lost access to the multiplayer game. By the end of December, after more than one month from the release date, i had been able to play only a few times in one week and with a lot of problems. I searched for help from my ISP, friends, steam forums, and every other known AC forum without success. First i had a lot of NAT issues, at home i always got a Red NAT and most of the time i wasn't able to even start a game, but, mysteriously i was able to play on public networks. I started playing this game on single player mode on the first day it was released without any major problems, but, a few days later i found out that i wasn't able to play the multiplayer game. On November 16, 2013, i bought Assassin's Creed Black Flag Digital Deluxe Edition Pre-Order, later, on November 22, 2013, i also got Assassin's Creed Black Flag Season Pass on Steam store.

Where does my ubisoft activation code come from