I'm sorry to hear about this experience and I know the situation can feel very overwhelming and upsetting. The fact that someone may have gained access to your in-game account through your authenticator indicates a more serious issue in that your email account may also be compromised. First, you'll want to secure your computer, then secure your account to make sure the hijacker will be unable to access your account again.
You'll notice that after your computer has been secured, step one of securing your account involves changing your login details for your email address and also protecting your email with authenticator for additional security.
An account is only as secure as we make it using the tools available to us and the responsibility lies on us to maintain account security - not Jagex. I hope you will come back after things have cooled off a bit and take a little bit of time to implement these security measures so that you may once again enjoy RuneScape.
@ WorldsGr8est - It is understandable that you are upset over what happened to your account. However, the language used in your post is not appropriate for the Forums, and as a result your post has been hidden.
I do hope you take Spearmint30's advice above and get your email and account secured and give the game another chance. If you need additional security advice, the Community Led Account Help Forum is the best place to post for that.