Here is a collection of stock firmware for Vodafone Smart Ultra 6. If you find any missing/updated firmware or receive any OTAs, please post it to this thread. Updates are available at ZTE support site.
Do not use TWRP to flash stock firmware! You'll find update.zip and installation instructions within each package. Use stock recovery that is compatible with your stock firmware to install (stock recovery images are in TWRP flashable zips).