To reply to one of the people here, DPRK does have "internet", but they call it intranet over there. North Korea's intranet 광명 does NOT allow access to websites the global internet would offer like Google. So 윤세리 cannot get on Google Voice and tell everyone she's okay. There is a very small fraction of elites who do have access to the global internet. There is a chance 리충렬 could have access to the global internet considering his position in the government, but there is a very slim chance 리정혁 would be given this luxury as well despite his family status. And I doubt his father would help him by letting him use the global internet for a multitude of reasons.
P.S. I rate the show 5/5 stars in reality. This is just a reply to someone.