Why was my account banned? I didn’t cheat…How to unblock an account
You can not get help for this on the forums, you will need to send in a ticket to support. support.gaijin.net
Chances are that you never ever cheated, BUT you gave your account to your good friend, who may actually have done something fishy with it. And that is not your fault. At least that is the general pattern unfolding here over the last few days.
I hate it when I let my friend play for one round and in that time he downloads sophisticated cheat programs and grinds my tech trees to the top and gets me banned.
As Ravanos already mentioned, please contact with Support via ticket.