Hi,
Please check if your prepaid plan comes up with specific APN's.
They should be entered in Network > Mobile and deselect Auto APN to enter Custom APN.
Also, do you know for sure that these SIM cards have been activated and are working with modems? It might be that operator does not allow these data SIMs to work on the modems.
Does it say that you're registered to operator and mobile data, or just operator registered and data shows as disconnected?
EB.
