Hey u/Arcaluck,
Unfortunately, the advice you've received from others is correct, with a Jagex account, there is no manual way to recover it.
In order to have had your email account changed, hijackers would have had to have been able to log in by entering the Jagex account email and password, and authenticating their login via the e-mail.
This suggests to me that your e-mail address itself is compromised, so I would highly suggest ...
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