If your only pieces of hardware are
1 ZTE MF636 USB 3G/GPRS modem
1 PoE Injector (to put power onto the Ethernet cable)
1 Network Camera using PoE for power
It sounds like you are trying to wirelessly connect your IP camera to a network (or make it available.
However you are don't going to be able to do it with this equipment, the ZTE MF636 is designed for connecting laptops (to desktops) wirelessly to the internet. The laptop has aUSB stack and a driver for the ZTE MF636, none of the pieces of equipment you have have a USB stack and even if they do they certainly don't have a ZTE MF636 driver.
You are trying to connect several peripherals together with no computer but on the whole USB peripherals are unusable without a computer containing drivers (except for memory sticks).
You probably need something like HR4110 from
Digi. Although they are not cheap (£200 - £300) so you may want to hunt around for something cheaper.
If your PoE switch port has a USB port then it is likely that it is for firmware upgrades and only supports USB memory sticks unless the data sheet/user manual for the product says differently.