Probably abit late, although, I wanted to add the following from what I've found and discussed with other chair users:
Currently if you're shadow banned the duration is either 4 hours or exactly 7 days from the date you received it. After the shadow ban is over your HWID flagged for a week and if you hit the kill limit (10-12+ kills) you'll be shadow banned again for the 4 hours or-so period. The reason you receive a 7 day shadow ban is when you're spam reported.
I just came back from a month break and was dropping 20+ kills most games, I even managed to get 34 in one game and was fine until I decided to play SND and went abit over-board sitting in SB waiting room again looking at 1 week ban with 1 week HWID flag thereafter.
Lastly, I've heard having an aged account helps a lot as Activision may have a trust factor with newer accounts to stop people getting permed (unheard off) and hopping on fresh accounts.
Probably abit late, although, I wanted to add the following from what I've found and discussed with other chair users: