Where did you send the email?
Try: feedback (at winamp.com)
Be sure to include the gmail account associated with your purchase.
The google order number from Google Wallet would also help....
Was it the in-app upgrade from free to Pro?
Or did you purchase the separate Winamp Pro stub
It's all pretty much automated with the Android Market / Google Play.
For the in-app upgrade, (re)install the free version:
As long as you are logged into the same Google aact on your phone with which you made the purchase, then it will automatically recognize that you've already upgraded to Pro.