Here, read this announcement and tell me if the email you got is that one? If so, you got phished. Just as Alteranz said, Jagex will never email you regarding bans or offenses. Sorry, try to be more careful next time.
You got phished. The "email from Jagex" was from a phisher leading to a fake rs website. Apparently you've been living under a rock lately since half the threads on this forum lately have been about people getting phishing emails.
Another nub bites the dust...