Or you could check the email that you used to apply for your steam account. The information of the purchase should have been sent to your email address, that is, if you haven't deleted it. I just went into my email address and remembered that steam sends you the purchase information as well in an email.
If that doesn't work than your only option is a new steam ID and a new purchase of CS:S.
In the future, might not want to tell anyone ANY detail about your steam. Even the username is enough for someone to get the further needed information to scam you. Also, try not to create a username that matches your email address, that's just asking for trouble there.
Anyways, try looking in your email folders and see if you can find the purchase information that steam sends. I found mine, so you should be able to find yours if you haven't trashed it already.