I think you've been scammed, when you checked your JaGex inbox did you use the links provided in the email?

If so there is a chance they have tricked you, kind of like this

www.runescape.com

If you went directly to www.runescape.com then you should be safe, as it's been said, JaGex NEVER email you, the only way they can find your email is when you sign up to members with a credit card and if they have taken your email from that then you are able to sue them, there are obviously laws against this, I doubt it is real though, if you went on them links change your password now!