It sounds like this issue is related to the mobile provider and the mobile plan, not the Digi device(s). My best suggestion at this point is to contact the mobile provider(s), give them the serial numbers (IMEI/MEID/ESN, whatever they need) of the devices in question, and information about any SIM cards if you're using any, and have them tell you what (if any) limitations the serial numbers / SIM cards have, for example outbound only, bi-directional, can they only talk to other devices on the same (mobile provider) network, etc.