HOW AVIS ****** ME

I've been charged R8000 (AUD800) a couple of weeks after giving my car back. I struggled to find out why, it appears that they had to do some repairs. I never saw any receipt, invoices or details about it. THEY JUST ****** ME. THAT'S IT!!! No more no less. I'm launching a Small Claim in Court to start with and my Lawyers (Slater & Gordon) are willing to take it further if anyone else had the same issues.