Doesnt save and deletes video

I taped important events of my childrens performances, and on several occasions it would say it saved the video, but when I would try to view it , it wasnt there. Also, when I updated my phone, EVERY SINGLE one of my previously saved viideos deleted, sort of like all the high scores on the kids games that do not save from version to version. Lost my video of when they won US Finals!!!
Did like the zoom video funtion though.

Deleted all my videos about Camera Zoom 4, v3.1