Do you have an alias email address? It might be that the email you are logging in with is different from the email the invitation to Klaus got sent to. When using the wrong email to access the account, you create a new empty Klaus account instead. What you need to do:
Find your Klaus invite.
Make sure to use the link on the invite to log into Klaus.
Log in and your emails will be merged to the same Klaus account.
Check which login method you are using. If you have set up a password + email login method, then you will be able to access your account only by using that info. You can later on add different login methods, such as the Google login.
Pro tip! Using 'Sign in with Google' is always the easiest and quickest option.
Go to Settings > Personal > Logins and you can merge the two accounts.
Please note, it's possible to change only your own login methods, and not for other users.