You now login with your registered email address and your password, both on the website and in the game as of July 2, 2019. Your account name is no longer required. New players creating accounts won't even have the option to create an account name. I wanted to let you know the reason for this change as quoted by a CM on the forums: "The main purpose was to simplify the login process, both for players in the long run and also for us development-wise and from a technical point of view. Account names were a remnant of the past and they have generated several issues over time."
If you still know the account name and the password of your account but don't know the email address, you can use the Lost Account Interface to request your account's email address. You'll be able to recover your account that way instead. I recommend always reading the support FAQ on Tibia's website if you're having trouble accessing your account as typically the answer is there.
Outstanding Contribution contestSeptember 14, 2020
Hints for posts that received a down-voteAugust 15, 2020
I've received a down-vote - how can I fix it?August 14, 2020
Interview with Benjamin Zuckerer - managing director at CipSoftMay 07, 2020