"usb modem" is not a valid model number. That terms simply tells you it connects via the usb port and that it's a modem, ie: a term that could apply to hundreds of devices.
"Vodafone K3565-Z", "K3520-Z", "ZXDSL 831 AII", and "MF622" would be valid ZTE USB modem model numbers.
ZTE support (or rather lack of)
Why a million dollar company like ZTE (a Chinese vendor) has a 10 cent support dept is beyond me.
Maybe it will change once you register (which is what it appears to be wanting before offering any support).
Why anyone would want to use a modem via the USB port (instead of the ethernet port where no driver is required) is also beyond me.
Look on the bottom and back side of the device. I'm sure you can find the model number if you look.
And you might check this list: http://list.driverguide.com/list/company3282/index.html