Check your spam/junk folder first. Make sure you're checking the most recent email if you requested more than one — only the latest code or link stays valid, and requesting a new one invalidates the previous one.
Enter exactly the digits shown in the email, with no spaces. If it still says the code is incorrect, request a new one — codes expire after a short time.
Make sure you're logged into the same account you purchased with, then try the "Restore Purchases" button on the Premium page. If it still doesn't appear, email us with your purchase receipt and account email.
Go to Settings (or Profile) → Delete Account inside the app. This immediately removes your account and all associated game data. If you're unable to access the app, email fbcenterofficial@gmail.com with the email address on your account and we'll process the deletion manually within a few days.