First, check that you're trying to sign in with the Microsoft account that is associated with your developer account. If you are, you might see a prompt indicating that your email is used with more than one account; in that case, choose Personal account to continue. If you don't see the prompt, and you're sure you are using the right Microsoft account, contact support.
Note. If your organization uses Azure Active Directory to allow multiple users to access a developer account, make sure that you're trying to sign in with the email address that your organization used to grant you access to the account, rather than signing in with a Microsoft account. If you're still having problems, contact your organization's Azure AD administrator for assistance.