Unless you've entered the email yourself, there is no real way to know what the Parental Controls email is.
I would suggest contacting support again, preferably by phone. I had the exact same problem that you did, in that I was prevented from posting on the D3 beta forums because my Parental Controls settings disallowed me. I tried to get the email, but like you, it never came to my inbox. This was not simply a case of Parental Controls not being set up, as they were, but I was not receiving the email.
After calling Blizzard Customer Support, they told me that my Battle.net account had apparently been compromised. Seeing as I'm not a WoW player and had no other assets to steal, whomever had hacked my account had decided to change my Parental Controls settings and email ("to be mean", in the words of the Support Representative).
This sounds potentially like the same thing, so I would urge you to contact support by phone (US info, EU info). Make sure you know the answers to your account security questions, and I would consider securing your account further with an authenticator, if you don't already have one.