Ending confusing

Has anyone read '59 minutes' by Holly Seddon? I couldn't make sense of the ending. It seemed to me that the author had written the three different threads to the story independently of each other and confused herself about the names of some characters and also about the timelines. Maybe it's me, so if anyone can explain, I'd be grateful. I was also puzzled about why the electricity and mobile phone networks are switched off immediately the incident started and thought the coincidence of important characters being whee they were was a bit far-fetched! I'd really appreciate anyone else's viewpoint.