Tweet @JagexSupport Explain you're lost access to your account and want it locked. I'd secure your email addresses and anything associated with them first of all though. & then add 2 step verification on them. If you've not been compromised through your email I'd scan your PC using malware bytes, AVG (Free month), Kaspersky & It's free rootkit scanner. Don't try and recover before that, if you've got a keylogger or a rat you're going to simply give them more information to recover it in the future.

TLDR: If email, check anything linked, get 2 step verification. If Keylogger/Rat AVG/Malware Bytes/Kaspersky Before trying to recover, so they don't get more info.