@asatorsbabe: Can you try Swiping up from your Home Screen > Open the the Contacts app > Select your parents number > Tap the 3 dots in the bottom right, and select 'Unblock contact' if applicable. If the problem persists, try heading to the Phone app > Tap the 3 dots in the top right > Settings > Supplementary Services, and check your Call Forwarding and Call Barring settings. Furthermore, head to Settings > Connections > Flight Mode, and toggle this off if it is active.
