https://support.steampowered.com/kb_...2347-QDFN-4366
this is what steam support says about the issue; sorry if it's not much more help than what you've already attempted, but it does remind you on several occasions to remember not to pass you account to anyone, and to review any instances in your gaming past when someone was allowed to access your account with your permission.
sadly, if someone's hacking on the account, we'd have no choice but to take action and ban the account from returning to any straferight servers. hopefully your account issues will be resolved through steam. in the meantime, we'll keep an eye out on your name. if it does occur, you can provide us with a steam ID and we'll look into it.
otherwise, a new account is the only sure-fire way of making sure it's 100% yours.
-DanFortH
My Steam Acct Has Been Highjack 
