okay so i have a vodafone smart v8 and recently (17/04/18) it wanted me to update (VFD-710 MRB01-3) so i did and so far all its done is stopped the home button from working, removed everything from my start screen, deleted contacts, logged me out of everything, and when i go to use thefinger sensor it says there isn't any finger prints registered so when i go to register it i get a message saying this finger print is already added.. what can i do?
Sounds a lot like it wasn't a update from the manufacturer but something else.
If that is the case, then try starting up the phone in "Safe Mode" and see if it will start ok. It will have limitations in that mode, but if the system works fine, and things are there that were not before, then you need to try running antivirus or malware detection and removal software to clean it up.
That or save your files and personal data (can't save apps) and then do a "Hard Reset" on the phone to start it over and remove anything that could be on it.
To get into "Safe Mode" please do the following.
1. First turn off the phone.
2. Next press and hold "Power" until you see the manufacturers logo on the screen, then release the power button.
3. "Quickly" press "Volume Down" and hold it for few seconds until you see the message "Safe mode: ON" or something similar.
4. If you wanted disable it, simply repeat the steps above, and you should see "Safe Mode: OFF" rather than on.