Change APN Type / T-Mo Hack? Netgear LB1120

[Jwidgeon]

I have a Netgear LB1120 with a T-Mobile Sim Card.... which worked great (20+ mbps download) until the hotspot data runs out. After that, it kicks down to 600kbps and is insanely slow. 

I read there are plenty of workarounds for this using a phone (Adding "dun" as an APN type supposedly works), but can't seem to find a fix when using a 4G modem - since there isnt a field for an APN type.

I have tried Express VPN both on my router and on a device (firestick) on separate occasions and that doesnt work. It drops the speeds so bad that even if it is bypassing the hotspot data it remains unusable. 

Does anyone have any potential fixes I can try to "trick" T-Mobile in to thinking its using smartphone data?

See attached image for the messages I'm receiving from T-Mo about the plan.