You can just let the account go just dont log it and thats that;however, I suggest you build other cities farther away from him and then let him do as he pleases while you build up troops in a separate city(s) then scout him see how many troops he has and strike back also go around and find the people he has colonized and band together with them to form resistance, speaking in world chat costs speakers ($$$) for one reason to make it hard for ppl that like to spam its a draw back but if you ever play a game where WC is free you will see that spam is everywhere just watch WC and wisper to the ppl there talking thats free. Also search forums here for guides on various subjects you are trying to learn it takes about a month to begin understanding this game and some research in your academy takes 2 weeks or more so its a game for the long term thinker. Best of luck msg me if you need help.