Did they ever resolve your problem? Same thing is happening to me. I purchased a Tab 2 several weeks ago and set up an account on Samsung. In order to download apps from Samsung, I had to go through the account. The account worked for a while, then it suddenly stopped working last night - it kept saying my password was incorrect.
Thinking somehow I forgotten it, I tried going to Samsung support to reset it. But, I'm getting the same thing you got - from both the "Get Email" and the "Get Password", it says "No matching information". Yet, when I tried using my email to sign up again from that same support site (one that requires the birthdate), it says the email is already in use.
I finally found a link to a live chat with Samsung support, and the person was useless. He said they couldn't look up my email and wouldn't explain what he meant by that. Then all he could tell me was to create a new account and disassociate my Tab 2 from the old account. But, I told him that when I do that, it gives me a warning that it will delete all data associated with the account! So, not a good solution, especially if this happens again, and Samsung still can't explain why my account suddenly goes haywire!
The Samsung guy said he doesn't what was wrong with my old account, just to create a new one, which would get rid of my data. However, since he didn't know what went wrong, he couldn't guarantee me that the same thing won't happen with the new account. And this time, I might have critical data I will lose if I have to again delete an account and create a new one!