Unless they have changed their practice, calling their tech support to activate the static IP (after paying $500 for the account) for those SIM cards you want to make static results in a static IP assignment that will show up the next time the SIM card(s) reconnect. The APN will also change (but current practice avoids you having to do anything in that regard).
There is the alternative of setting up a FusionHub solo on a server farm and connect your Transit to the hub via SpeedFusion. Vultr and UpCloud are two good, inexpensive ($5/month) choices, and they provide the static IP. @MartinLangmaid has provided extensive guidance regarding how to set it up (it is easy). E.g. Accessing device behind BR1 using FusionHub - #2 by MartinLangmaid
Good luck.
Z