It sounds like you may have started the enrolment process but are not yet finished. Using a web browser (preferably Google Chrome) on a computer, go to www.league.com and sign in with your email address and password. You should be signing in with the email address that your League invitation email was sent to.
If you're still having issues, reach out to our Customer Care team via email at email@example.com. Our agents will be able to help you finish the enrolment process!