Psát samozřejmě můžeš, ale šance na unban je prakticky nulová. Třeba jsem našel tuhle reakci zabanovaného:

You won't get unbanned. I contacted Steam support after my account was hijacked and used for cheating, I've got a VAC ban on csgo. It doesn't matter who was on your account if the ban is legitimate then it won't be removed. :(