If you see "notifications silenced" while messaging or calling them, it means they have put their iPhone in the Do Not Disturb (DND) mode, and they don't want to be disturbed for a certain period. There are various reasons why people put their iPhones in the Do Not Disturb (DND) mode, and one of the most common reasons is that they want to focus on completing a certain task without any disturbance. You may try contacting the person later If you are still getting the same message.