Most failed sign-ins are not account problems. Rule these out in order before contacting anyone: an email address that differs from the one used at registration; caps lock left on, or a browser autofilling an old password it saved months ago; a password reset email sitting unread in a spam folder.
Then the less obvious ones. An account that has not completed verification is restricted in what it can do rather than blocked from signing in, so if you can log in but cannot withdraw, that is verification and not access. A browser extension or an aggressive ad blocker can stop the sign-in form submitting. And a cached older version of the site can serve a form that no longer works, which a hard refresh clears.
If none of that applies, use live chat or write to the operator's support team — both run 24/7 and multilingual. Having trouble specifically on a phone is usually a browser issue rather than an account one, and our Lizaro mobile page covers what mobile play does and does not involve.