The new Steam "Family sharing" make it easy to become back your banned(Treyarch, VAC i dont know) Account.
Just make a new Account then You must have installed the banned game:
"Play.png"
Press on play and there Will open a Window, press on Request access:
"Request.png"
Go to your banned Account email:
"Email.png"
Then you can go to your Games and Enjoy!
USE AT YOUR OWN RISK