Krow
Crowman
first check the hardware version:
How to find the hardware version on a TP-Link device? - Welcome to TP-LINK
then update to that hardware version latest firmware:
TD-W8968 - Welcome to TP-LINK
make sure to read instructions first before updating firmware.
edit:check this video as reference for configuring EC306:
Unboxing TP-LINK MR3220 and How to Setting Huawei EC-306 rev.A + Flexi EVDO - YouTube
3G/4G USB Modem Compatibility List for TD-W8968 - Welcome to TP-LINK
The link above shows that EC 306 isn't supported.
I saw that video before trying to connect. Didn't work.