Apple

Last month I bought an iPhone se 1gen of 64gb because my phone got stolen and I needed a new one right away but one thing I noticed was that the system data that supposedly is cache data started filling up very fast and my phone just kept telling me that my storage was full and what I did was reset it multiple times but I'm not talking about resetting it once a month I'm talking about resetting it daily and everytime I reset it and set it up again it does the same thing over and over again and it only has one app downladed that is whatsapp and this is driving me crazy I've tried to restore it by iTunes to try a completely new apple id on it and it just does the same, does anyone have an idea of what's going on?