In this case, if you are sure about the account name, on the log in screen, you should be able to choose Reset my password option. By doing this, you can reset your password if you entered a wrong one and you didn't realized. If this isn't working, try making a new user account with the same contact information. By doing this you can check if you exist in the database or not. You can also contact the developer on the official contact page. The developer should be able to provide more information regarding this problem.