1. Please make sure whether the app that you previously signed up and the one you're logging in are the same;
2. Whether the country you select when signing up is the same as that when logging in;
3. Is the user name entered correctly? For instance, you misremembered the email account or password;
4. Please confirm the registration method at that time. For instance, you logged in with a social account at that time, but enter an email account now;
If the above problem does not exist after the investigation, please feedback.