I have an android mobile - Samsung galaxy J3 and a box asking me to update my system always appears when I switch on my wifi, I accidentally pressed on it and it started updating, I then took the battery out before it could install. Whenever I try to switch my phone on it keeps trying to update the system. I have tried to hold the power button, the home key and the volume key (tried both up and down) several times but it won't start up normally, it keeps asking me to download "A custom OS" which I don't want either. Any help please with what I can try. Thanks