Re: Banned for no reason
The simple and sad answer to your question is: Your account your responsibility, whatever happens on your account whether or not you performed or someone else performed an action that is against the terms of service is fully on you, so all the consequences of such actions are yours.
This is why you should always protect your account, and not let others use it.
As far as how that impacts your relationship with your cousin that is between the two of you.