Screwed over in an account bought from DaOrville

So... Second account I have bought trying to get started on a new main since jagex basically screwed me on an account I've had since 2004 and have since been screwed again here. $275 this time. I bought the account a few months ago, I have been playing a bit and go to log in today and the person I purchased from has changed the password, I tried to pm on here which apparently I'm not allowed to and tried on discord, finally getting a response when posting on their profile to take it up with the admins here. So what do I need to do?

I have screen shots and all that as well, just need specifics on what I need to post.

 

Link to profile:
DaOrville

Explanation of the trade:
He explained he would keep the account in his email and such to keep a warranty on it incase it was lost or stolen he could retrieve it. Said I could set an authentication code and all as well which I did. Agreed on $275. Now a couple months later I'm not able to log in due to password change and was told to take it up with the admins.

Amount scammed:
$275

How they scammed:
Changed password a couple months after purchase and told me to deal with admins.

Discord ID:
DaOrville#8811

Uploading screenshots to dropbox now.