When selecting the Call Me option, at the Duo prompt on the Central Authentication Service (CAS), a status message indicates Answered. Press any key on your phone to log in. but your phone doesn't ring or indicate a missed call. 

After a period of time, the status message indicates Error during call: No keys pressed.

Duo Multi-Factor Authentication (MFA).

Restart the phone and try the Call Me method again.

Calls from (301) 405-1500 are going directly to the phone number's voicemail without ringing the phone, and (301) 405-1500 is not blocked on your phone.